Battery cell engineering and design to reach high energy

ABSTRACT

Improved high energy capacity designs for lithium ion batteries are described that take advantage of the properties of high specific capacity anode active compositions and high specific capacity cathode active compositions. In particular, specific electrode designs provide for achieving very high energy densities. Furthermore, the complex behavior of the active materials is used advantageously in a radical electrode balancing design that significantly reduced wasted electrode capacity in either electrode when cycling under realistic conditions of moderate to high discharge rates and/or over a reduced depth of discharge.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of copending U.S. patent applicationSer. No. 13/464,034 filed on May 4, 2012 and published as US2013/0295439A1 to Masarapu et al., entitled “Battery Cell Engineeringand Design to Reach High Energy,” incorporated herein by reference.

GOVERNMENT RIGHTS

Development of the inventions described herein was at least partiallyfunded with government support through U.S. Department of Energy grantARPA-E-DE-AR0000034 and California Energy Commission grant ARV-09-004,and the U.S. government has certain rights in the inventions.

FIELD OF THE INVENTION

The inventions, in general, relate to high energy lithium batterieshaving silicon based high capacity negative electrode balanced with highcapacity positive electrodes that can be designed to provide high energyoutput and long cycle life. The invention further relates to electrodeswith conductive additives such as carbon nanotubes, in which theelectrode have high percentage of active material, high loading levelsand high densities to achieve high energy densities when incorporatedinto cells.

BACKGROUND

Lithium batteries are widely used in consumer electronics due to theirrelatively high energy density. Rechargeable batteries are also referredto as secondary batteries, and lithium ion secondary batteries generallyhave a negative electrode material that incorporates lithium when thebattery is charged. For some current commercial batteries, the negativeelectrode material can be graphite, and the positive electrode materialcan comprise lithium cobalt oxide (LiCoO₂). In practice, only a modestfraction of the theoretical capacity of the positive electrode activematerial generally can be used. At least two other lithium-basedpositive electrode active materials are also currently in commercialuse. These two materials are LiMn₂O₄, having a spinel structure, andLiFePO₄, having an olivine structure. These other materials have notprovided any significant improvements in energy density.

Lithium ion batteries are generally classified into two categories basedon their application. The first category involves high power battery,whereby lithium ion battery cells are designed to deliver high current(Amperes) for such applications as power tools and Hybrid ElectricVehicles (HEVs). However, by design, these battery cells are lower inenergy since a design providing for high current generally reduces totalenergy that can be delivered from the battery. The second designcategory involves high energy batteries, whereby lithium ion batterycells are designed to deliver low to moderate current (Amperes) for suchapplications as cellular phones, lap-top computers, Electric Vehicles(EVs) and Plug in Hybrid Electric Vehicles (PHEVs) with the delivery ofhigher total capacity.

SUMMARY OF THE INVENTION

In a first aspect, the invention pertains to a lithium ion secondarybattery comprising a positive electrode, a negative electrode, aseparator between the positive electrode comprising a lithium metaloxide and the negative electrode comprising a lithiumintercalation/alloying composition, supplemental lithium in an amountwith an oxidation capacity corresponding to 0% to 110% of theirreversible capacity loss of the negative electrode and an electrolytecomprising lithium ions. In some embodiments, during the first initialactivation charge, the battery has a negative electrode charge capacityof about 75% to about 99.5% at a rate of C/20 from the open circuitvoltage to 4.6V relative to the sum of the positive electrode chargecapacity at a rate of C/20 from the open circuit voltage to 4.6V plusthe oxidation capacity of any supplemental lithium. Following activationof the battery in a first charge cycle the positive electrode can have aspecific discharge capacity of at least 180 mAh/g with respect to theweight of the positive electrode active material, the negative electrodecan has a specific discharge capacity of at least 700 mAh/g with respectto the weight of the negative electrode active material at a rate of C/3discharged from 4.5V to 1.5V, and the battery can have a dischargeenergy density of at least about 250 Wh/kg at C/3 when discharged from4.5V to 1.5V.

In another aspect, the invention pertains to lithium ion secondarybattery comprising a positive electrode, a negative electrode, and aseparator between the positive electrode and the negative electrode, inwhich the positive electrode has a density in the range of about 2.2g/mL to about 3.3 g/mL and a loading level of positive electrode activematerial on a current collector that is from about 10 mg/cm² to about 30mg/cm², and in which the negative electrode comprises a high capacitynegative electrode active material with a discharge specific capacity ofat least about 700 mAh/g at a rate of C/3, has a density in the range ofabout 0.4 g/mL to about 1.3 g/mL, and has a loading level of negativeelectrode active material that is at least 1.5 mg/cm². The battery canhave a discharge energy density at the 50th charge-discharge cycle of atleast about 250 Wh/kg at C/3 when discharged from 4.5V to 1.5V.

In a further aspect, the invention pertains to a positive electrode fora lithium ion secondary battery comprising from about 90 wt % to about96 wt % positive electrode active material, from about 2 wt % to about 6wt % polymeric binder, and from about 0.5 wt % to about 8 wt % carbonnanotube as conductive additive. In some embodiments, the positiveelectrode can have a specific discharge capacity of at least 180 mAh/gat C/3 from 4.6V to 2V against lithium.

In an additional aspects, the invention pertains to a negative electrodefor a lithium ion secondary battery comprising from about 60 wt % toabout 90 wt % of a high capacity negative electrode active material,from about 8 wt % to 30 wt % of a polymeric binder, and from about 1 wt% to 15 wt % conductive additive. In some embodiments, the electrode canhave a specific discharge capacity from about 1.5V to 5 mV againstlithium of at least 700 mAh/g at C/3.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view of an electrode stack useful forthe formation of a battery.

FIGS. 2( a)-(c) have the following views: (a) is an exploded view of apouch battery with a battery core separated from two portions of thepouch case; (b) is a perspective lower face view of the assembled pouchbattery of (a); and (c) is a bottom plan view of the pouch battery of(b).

FIG. 3 is a plot of discharge capacities versus cycle number ofbatteries with a lithium foil electrode and silicon based counterelectrodes with four different compositions.

FIG. 4 is a plot of discharge capacity versus cycle number of batterieswith a lithium foil electrode and silicon based counter electrodes withthree different electrode densities.

FIG. 5 is a plot of charge and discharge capacities versus cycle numberof batteries with a lithium foil electrode and counter electrodes madefrom different silicon based materials.

FIG. 6 is a plot of charge and discharge capacities versus cycle numberof batteries with a lithium foil electrode and positive electrodes madewith two different conductive additives.

FIG. 7 is a plot of discharge capacity versus cycle number of batterieswith a lithium foil electrode and positive electrodes with variouselectrode loading levels having an electrode density of ≦3 g/mL, inwhich varying electrode loading is obtained by selecting an appropriatethickness of the electrodes.

FIG. 8 is a plot of charge and discharge capacities versus cycle numberof a battery with a lithium foil electrode and positive electrode withan electrode loading of 26 mg/cm² and electrode density of 2.4 g/mL.

FIG. 9 is a plot of discharge capacity versus cycle number of batterieswith different balance of SiO—Si—C anode against HCMR™ cathode with andwithout supplemental Li added to the negative electrode.

FIG. 10 is a plot of discharge capacity versus cycle number of pouchcell batteries having an approximate 10 Ah design capacity, with andwithout supplemental lithium.

FIG. 11( a) is a plot of discharge capacity versus cycle number of a 20Ah capacity pouch cell battery with supplemental lithium cycled up to200 cycles.

FIG. 11( b) is a plot of energy density per kg versus cycle number ofthe battery of FIG. 11( a).

FIG. 12( a) is a plot of discharge capacity versus cycle number of apouch cell battery with supplemental lithium having approximately 48 Ahdesign capacity cycled up to 500 cycles.

FIG. 12( b) is a plot of energy density per kg versus cycle number ofthe battery of FIG. 12( a).

FIG. 12( c) is a plot of volumetric energy density per liter versuscycle number of the battery of FIG. 12( a).

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Battery designs have been developed to take particular advantage of highspecific capacity active materials used in both the positive electrodeand the negative electrode. In particular, important design parameterswith the appropriate values have been identified to achieve a highperformance with respect to capacity, power, rate capability andcycling. Identification of appropriate cell design and electrodeparameters has been found to be very significant in obtaining consistentgood performance across selected performance parameters. Negativeelectrode active materials of particular interest can be silicon basedmaterials with a large specific capacity relative to graphite.Specifically, significant advances have been made with respect tonanostructured elemental silicon as well as silicon suboxides thatprovide significantly improved cycling properties relative to bulkelemental silicon. Correspondingly, high capacity positive electrodeactive materials have also been developed that can provide good cyclingproperties for a very large number of cycles at reasonably highcapacities. It has been discovered that by effectively combiningimproved capacity materials in both electrodes with a selected balanceof the electrodes and with appropriate electrode loading and densitypreserves cycling and provides for efficient battery architecture andgood rate performance of the battery. In some embodiments, it has beenfound that supplemental lithium added to the battery can compensate forhigh first cycle irreversible capacity loss and to significantly improvecycling of the batteries. Furthermore, carbon nanotubes have been foundto improve cycling performance when used as an electrically conductiveadditive. Pouch batteries are described that take advantage of thesedesign improvements to achieve high energy performance of a batterybased on both weight and volume of the battery.

Lithium has been used in both primary and secondary batteries. Anattractive feature of lithium metal for battery use is its light weightand the fact that it is the most electropositive metal, and aspects ofthese features can be advantageously captured in lithium-based batteriesalso. Certain forms of metals, metal oxides, and carbon materials areknown to incorporate lithium ions into the material throughintercalation, alloying or similar mechanisms. Lithium ion batteriesgenerally refer to batteries in which the negative electrode activematerial is also a lithium intercalation/alloying material. If lithiummetal itself is used as the anode, the resulting battery generally isreferred to as a lithium battery.

If elemental lithium metal itself is used as the anode or negativeelectroactive material, the resulting battery generally is referred toas a lithium battery. Lithium batteries can initially cycle with goodperformance, but dendrites can form upon lithium metal deposition thateventually can breach the separator and result in failure of thebattery. As a result, commercial lithium-based secondary batteries havegenerally avoided the deposition of lithium metal through the use of anegative electrode active material that operates throughintercalation/alloying or the like above the lithium deposition voltageand with a slight excess in negative electrode capacity relative to thecathode or positive electrode. The batteries described herein arelithium-based batteries in which a non-aqueous electrolyte solutioncomprises lithium ions. For secondary lithium ion batteries duringcharge, oxidation takes place in the cathode (positive electrode) wherelithium ions are extracted and electrons are released. During discharge,reduction takes place in the cathode where lithium ions are inserted andelectrons are consumed. Similarly, the anode (negative electrode)undergoes the opposite reactions from the cathode to maintain chargeneutrality. Unless indicated otherwise, performance values referencedherein are at room temperature, i.e., about 23±2° C.

The word “element” is used herein in its conventional way as referringto a member of the periodic table in which the element has theappropriate oxidation state if the element is in a composition and inwhich the element is in its elemental form, M⁰, only when stated to bein an elemental form. Therefore, a metal element generally is only in ametallic state in its elemental form, i.e. elemental metal or acorresponding alloy of the metal's elemental form, i.e. metal alloy. Inother words, a metal oxide or other metal composition, other than metalalloys, generally is not metallic.

The battery designs herein take advantage of electrode designs based onrealistic electrode densities and loadings that can be achieved with thehigh capacity materials that have been developed. In particular, thedensity of the electrodes is desirably high to achieve a high overallcapacity for a weight of the battery while not making the densities sohigh that cycling performance is lost. Similarly, the electrode loadingsare selected to balance rate performance of the batteries with theoverall capacity. Based on these improved designs, batteries aredescribed with extremely high energy densities of at least about 250Wh/kg to energy densities exceeding 400 Wh/kg.

When lithium ion batteries are in use, the uptake and release of lithiumfrom the positive electrode and the negative electrode induces changesin the structure of the electroactive material. As long as these changesare essentially reversible, the capacity of the material does notchange. However, the capacity of the active materials is observed todecrease with cycling to varying degrees. Thus, after a number ofcycles, the performance of the battery falls below acceptable values,and the battery is replaced. Also, on the first cycle of the battery,generally there is an irreversible capacity loss that is significantlygreater than per cycle capacity loss at subsequent cycles. Theirreversible capacity loss (IRCL) is the difference between the chargecapacity of the new battery and the first discharge capacity. Theirreversible capacity loss results in a corresponding decrease in thecapacity, energy and power for the battery due to changes in the batterymaterials during the initial cycle.

The decreasing battery capacity with cycling can have contributions fromthe positive electrode, the negative electrode, the electrolyte, theseparator or combinations thereof. The battery described herein combinepositive electrode and negative electrode with improved capacities toassemble a high energy battery that has high capacity and cyclingstability. It is useful to note that during charge/dischargemeasurements, the specific capacity of a material depends on the rate ofdischarge. The highest specific capacity of a particular material ismeasured at very slow discharge rates. In actual use, the actualspecific capacity is less than the maximum value due to discharge at afaster rate. More realistic specific capacities can be measured usingreasonable rates of discharge that are more similar to the ratesencountered during actual use. For example, in low to moderate rateapplications, a reasonable testing rate involves a discharge of thebattery over three hours. In conventional notation this is written asC/3 or 0.33 C. Faster or slower discharge rates can be used as desired,and the rates can be described with the same notation.

The positive electrodes can exhibit a significant first cycleirreversible capacity loss. However, high capacity silicon-based anodescan generally exhibit contributions to IRCL significantly greater thanthe positive electrode active material. The design of the negativeelectrode active materials can be selected to reduce the IRCL, which canbe significant with respect to reducing the excess anode balance in thecell design. Also, the positive electrode active material can similarlybe designed to reduce IRCL associated with the positive electrode.Furthermore, supplemental lithium can be used as a substitute foradditional capacity of the positive electrode to compensate for therelatively large IRCL of the negative electrode. With appropriatestabilization of the negative electrode and positive electrode, abattery with high capacity materials in both electrodes can exhibit highspecific capacities for both electrodes over at least a moderate numberof cycles.

The advances described herein are built upon previous development of ahigh energy battery using high capacity lithium metal oxides asdescribed in published U.S. patent application 2009/0263707 to Buckleyet al. (“the '707 application”), entitled “High Energy Lithium IonSecondary Batteries,” incorporated herein by reference. The presentdevelopments significantly advance the designs of the '707 applicationthrough the identification of designs to take particular advantage ofincorporation of high capacity silicon-based active anode materials aswell as design improvements that accomplish long term cycling.Significant advance relates to the balance of the high capacity positiveelectrode properties with the high capacity negative electrodeproperties. With the high energy batteries described herein aregenerally based on high capacity positive electrode active materials,such as lithium rich lithium metal oxides described below. When usedwith high capacity negative electrode active materials, the loading on acurrent collector is generally increased to obtain the high energy ofthe battery without excess weight and volume associated with moreelectrodes in the battery stack. However, loading and electrodedensities are limited by performance properties. In particular, cyclingperformance degrades if the density of the cathode is increased toomuch, and capacity can decrease if the loading is increased too much. Asfound herein, the use of improved electrically conductive additives,particularly carbon nanotubes, can increase performance parameters forspecific loadings and densities for both the positive electrode andnegative electrode.

High capacity negative electrodes can be formed with silicon-basedactive materials. These materials can supply very high capacity withreasonable cycling properties. With the high capacity negativeelectrodes, the electrode designs involve appropriate selection ofloading, density and electrically conductive additives. To achievedesired cycling properties, the balance of the negative electrodecapacity to the positive electrode capacity can be adjusted with areasonable amount of excess negative electrode capacity, and the balanceof the positive electrode and negative electrode very significantlyinfluences performance. To achieve improved cycling, supplementallithium can be included in the battery.

The high capacity negative electrode active materials generally have alarge irreversible capacity loss resulting from the firstcharge-discharge cycle. It has been found that the addition ofsupplemental lithium can effectively compensate for this loss ofcapacity. It has also been found that supplemental lithium can improvethe cycling performance of lithium rich high capacity lithium metaloxides in the cathode. In particular, the compensation of theirreversible capacity loss for the high capacity anode materials isdescribed further in published U.S. patent application 2011/0111294 toLopez et al. (the '294 application), entitled “High Capacity AnodeMaterials for Lithium Ion Batteries,” incorporated herein by reference.The use of supplemental lithium to improve the cycling properties ofhigh capacity lithium rich cathode materials is described further incopending U.S. patent application Ser. No. 12/938,073 to Amiruddin etal. (the '073 application), entitled “Lithium Ion Batteries WithSupplemental Lithium,” incorporated herein by reference. Supplementallithium, for example, can be supplied by elemental lithium, lithiumalloys, a sacrificial lithium source or through electrochemicallithiation of the negative electrode prior to completion of the ultimatebattery. Some high capacity negative electrode active materials havelower irreversible capacity loss, and for batteries with thesematerials, supplemental lithium may or may not be desirable tocompensate for loss of lithium.

The high energy batteries described herein can achieve high values ofenergy density and volumetric energy density. Pouch cell formats areparticularly desirable due to their efficient weight and volumepackaging. Using high specific capacity materials described herein, thehigh energy densities can be reasonably maintained during cycling. Thebatteries are suitable for a range of commercial applications, such aselectric vehicles, consumer electronics and the like.

Battery Structure

Referring to FIG. 1, a battery 100 is shown schematically having anegative electrode 102, a positive electrode 104 and a separator 106between negative electrode 102 and positive electrode 104. A battery cancomprise multiple positive electrodes and multiple negative electrodes,such as in a stack, with appropriately placed separators. Electrolyte,such as the desirable electrolytes described herein, in contact with theelectrodes provides ionic conductivity through the separator betweenelectrodes of opposite polarity. A battery generally comprises currentcollectors 108, 110 associated respectively with negative electrode 102and positive electrode 104. The stack of electrodes with theirassociated current collectors and separator are generally placed withina container with the electrolyte. In general, the lithium ion batterydescribed herein comprises a positive electrode comprising a lithiumintercalation material and a negative electrode comprising a lithiumintercalation/alloying material.

The nature of the positive electrode active material and the negativeelectrode active material influences the resulting voltage of thebattery since the voltage is the difference between the half cellpotentials at the cathode and anode. Suitable positive electrode activematerials and suitable negative electrode lithium intercalation/alloyingcompositions of particular interest are described in detail below.

The positive electrode active compositions and negative electrode activecompositions generally are powder compositions that are held together inthe respective electrode with a polymer binder. The binder providesionic conductivity to the active particles when in contact with theelectrolyte. Suitable polymer binders include, for example,polyvinylidene fluoride (PVDF), polyethylene oxide, polyimide,polyethylene, polypropylene, polytetrafluoroethylene, polyacrylates,rubbers, e.g. ethylene-propylene-diene monomer (EPDM) rubber or styrenebutadiene rubber (SBR), copolymers thereof, or mixtures thereof. Asdescribed in the '707 application cited above, high molecular weight(e.g., at least about 800,000 AMU) PVDF is a particularly desirablepolymer binder for the positive electrodes. Furthermore, thermallycurable polyimide polymers have been found desirable for high capacitynegative electrodes, which may be due to their high mechanical strength.The following table provides suppliers of polyimide polymers, and namesof corresponding polyimide polymers.

Supplier Binder New Japan Chemical Co., Ltd. Rikacoat PN-20; RikacoatEN-20; Rikacoat SN-20 HD MicroSystems PI-2525; PI-2555; PI-2556; PI-2574AZ Electronic Materials PBI MRS0810H Ube Industries. Ltd. U-Varnish S;U-Varnish A Maruzen petrochemical Co., Ltd. Bani-X(Bis-allyl-nadi-imide) Toyobo Co., Ltd. Vyromax HR16NN

With respect to polymer properties, some significant properties for highcapacity negative electrode application are summarized in the followingtable.

Tensile Strength Elastic Viscosity Binder Elongation (MPa) Modulus (P)PVDF 5-20% 31-43 160000 psi 10-40 Polyimide 70-100% 150-300 40-60 CMC30-40%  10-15 30

PVDF refers to polyvinylidene fluoride, and CMC refers to sodium carboxymethyl cellulose. The elongation refers to the percent elongation priorto tearing of the polymer. In general, to accommodate the silicon basedmaterials, it is desirable to have an elongation of at least about 50%and in further embodiments at least about 70%. Similarly, it isdesirable for the polymer binder to have a tensile strength of at leastabout 50 MPa and in further embodiments at least about 100 MPa. Tensilestrengths can be measured according to procedures in ASTM D638-10Standard Test Method for Tensile Properties of Plastics, incorporatedherein by reference. A person of ordinary skill in the art willrecognize that additional ranges of polymer properties within theexplicit ranges above are contemplated and are within the presentdisclosure. To form the electrode, the powders can be blended with thepolymer in a suitable liquid, such as a solvent for the polymer. Theresulting paste can be pressed into the electrode structure.

The active material loading in the binder can be large. In someembodiments, the positive electrode comprises from about 85 to about 98%of positive electrode active material, in other embodiments from about88 to about 97% of the positive electrode active material, and infurther embodiments from about 92 to about 96% of the positive electrodeactive material. In some embodiments, the negative electrode has fromabout 60 to about 96% of negative electrode active material, in otherembodiments from about 70 to about 90% of the negative electrode activematerial, and in further embodiments from about 75 to about 85% of thenegative electrode active material. A person of ordinary skill in theart will recognize that additional ranges of particles loadings withinthe explicit ranges about are contemplated and are within the presentdisclosure.

In some embodiments, the positive electrode has from about 1 to about10% polymeric binder, in other embodiments from about 1.5 to about 7.5%polymeric binder, and in further embodiments from about 2 to about 5%polymeric binder. In some embodiments, the negative electrode has fromabout 2 to about 30% polymeric binder, in other embodiments about 5 to25% polymeric binder, and in further embodiments from about 8 to 20%polymeric binder. A person of ordinary skill in the art will recognizethat additional ranges of polymer loadings within the explicit rangesabove are contemplated and are within the present disclosure.

The positive electrode composition, and in some embodiments the negativeelectrode composition, generally can also comprise an electricallyconductive additive distinct from the electroactive composition. In someembodiments, to achieve improved performance a conductive additive canhave a conductivity of at least about 40 S/cm, in some embodiments atleast about 50 S/cm, and in further embodiments at least about 60 S/cm.A person of ordinary skill in the art will recognize that additionalranges of conductivity within the explicit ranges above are contemplatedand are within the present disclosure. Electrical conductivity, which isthe inverse of resistivity, is reported by distributors, and theconductivity is generally measured using specific techniques developedby the distributors. For example, measurements of carbon blackelectrical resistance is performed between two copper electrodes withSuper P™ carbon blacks, see Timcal Graphite & Carbon, A Synopsis ofAnalytical Procedures, 2008, www.timcal.com. Suitable supplementalelectrically conductive additives include, for example, graphite,graphene, carbon fibers, carbon black, metal powders, such as silverpowders, metal fibers, such as stainless steel fibers, and the like, andcombinations thereof. Carbon nanotubes have been found to be a desirableconductive additive that can improve cycling performance for either apositive electrode or a negative electrode. In particular, for highloading levels of active materials in the electrodes, e.g., at leastabout 20 mg/cm², carbon nanotubes provided surprising improvement in therate capabilities of the resulting electrodes relative to electrodesformed with other electrically conductive additives even though theelectrical conductivities of the materials were similar.

In some embodiments, the positive electrode can have 0.5 weight percentto about 15 weight percent conductive additive, in further embodimentsfrom about 0.75 weight percent to about 12.5 weight percent, and inother embodiments from about 1 weight percent to about 10 weight percentconductive additive. Similarly, the negative electrode can have 1 weightpercent to about 20 weight percent conductive additive, in furtherembodiments from about 1.5 weight percent to about 15 weight percent,and in other embodiments from about 2 weight percent to about 10 weightpercent conductive additive. In some embodiments, the conductiveadditive used in the negative electrode is carbon nanotubes, although acombination of conductive carbon conductive additives can be used. Theconductive additive used in the positive electrode can also be acombination of electrically conductive additives listed above.Specifically, in some embodiments, the conductive additive used in thepositive electrode is a combination of carbon nanotubes with optionallyan additional conductive additive including carbon nanofiber,nanostructured carbon, graphene, KS6, Super-P, or a combination thereof.A person of ordinary skill in the art will recognize that additionalranges of amounts of electrically conductive additive within theexplicit ranges above are contemplated and are within the presentdisclosure.

The positive electrode and negative electrode used in the batteriesdescribed herein can have high loading levels that are balanced withreasonably high electrode density. For a particular loading level, thedensity is inversely correlated with thickness so that an electrode witha greater density is thinner than an electrode with a lower density. Insome embodiments, the negative electrode of the battery has a loadinglevel of negative electrode active material that is at least about 1.5mg/cm², in other embodiments from about 2 mg/cm² to about 8 mg/cm², andin additional embodiments from about 4 mg/cm² to about 7 mg/cm². In someembodiments, the negative electrode of the battery has a density in someembodiment from about 0.3 g/cm³ to about 2 g/cm³, in other embodimentfrom about 0.35 g/cm³ to about 1.6 g/cm³, and in additional embodimentsfrom about 0.4 g/cm³ to about 1.3 g/cm³. A person of ordinary skill inthe art will recognize that additional ranges of active material loadinglevel and electrode densities within the explicit ranges above arecontemplated and are within the present disclosure.

In some embodiments, the positive electrode of the battery has a loadinglevel of positive electrode active material that is from about 10 toabout 40 mg/cm², in other embodiments from about 15 to about 37.5mg/cm², and in additional embodiments from about 20 to about 35 mg/cm².In some embodiments, the positive electrode of the battery has an activematerial density in some embodiment from about 2.0 g/cm³ to about 3.3g/cm³, in other embodiment from about 2.2 g/cm³ to 3.1 g/cm³, and inadditional embodiment from about 2.3 g/cm³ to about 2.6 g/cm³. A personof ordinary skill in the art will recognize that additional ranges ofactive material loading level and electrode densities within theexplicit ranges above are contemplated and are within the presentdisclosure. In some embodiments, when the positive electrode or negativeelectrode uses a high loading level, the density of the electrode can bereduced to provide good cycling stability of the electrode. The densityof the electrodes is a function, within reasonable ranges, of the presspressures. Thus, the density of the electrodes cannot be arbitrarilyincreased without sacrificing performance with respect to loading levelswhile achieving desired cycling performance and capacity at higherdischarge rates.

Each electrode generally is associated with an electrically conductivecurrent collector to facilitate the flow of electrons between theelectrode and an exterior circuit. A current collector can comprise ametal structure, such as a metal foil or a metal grid. In someembodiments, a current collector can be formed from nickel, aluminum,stainless steel, copper or the like. An electrode material can be castas a thin film onto a current collector. The electrode material with thecurrent collector can then be dried, for example in an oven, to removesolvent from the electrode. In some embodiments, a dried electrodematerial in contact with a current collector foil or other structure canbe subjected to a pressure from about 2 to about 10 kg/cm² (kilogramsper square centimeter). The current collector used in the positiveelectrode can have a thickness from about 5 microns to about 30 microns,in other embodiments from about 10 microns to about 25 microns, and infurther embodiments from about 14 microns to about 20 microns. In oneembodiment, the positive electrode uses an aluminum foil currentcollector. The current collector used in the negative electrode can havea thickness from about 2 microns to about 20 microns, in otherembodiments from about 4 microns to about 14 microns, and in furtherembodiments from about 6 um to about 10 um. In one embodiment, thenegative electrode uses copper foil as current collector. A person ofordinary skill in the art will recognize that additional ranges ofcurrent collector within the explicit ranges above are contemplated andare within the present disclosure.

The separator is located between the positive electrode and the negativeelectrode. The separator is electrically insulating while providing forat least selected ion conduction between the two electrodes. A varietyof materials can be used as separators. Some commercial separatormaterials can be formed from polymers, such as polyethylene and/orpolypropylene that are porous sheets that provide for ionic conduction.Commercial polymer separators include, for example, the Celgard® line ofseparator material from Hoechst Celanese, Charlotte, N.C. Suitableseparator materials include, for example, 12 micron to 40 micron thicktrilayer polypropylene-polyethylene-polypropylene sheets, such asCelgard® M824, which has a thickness of 12 microns. Also,ceramic-polymer composite materials have been developed for separatorapplications. These composite separators can be stable at highertemperatures, and the composite materials can significantly reduce thefire risk. The polymer-ceramic composites for separator materials aredescribed further in U.S. Pat. No. 7,351,494 to Hennige et al., entitled“Electric Separator, Method for Producing the Same and the Use Thereof,”incorporated herein by reference. Polymer-ceramic composites for lithiumion battery separators are sold under the trademark Separion® by EvonikIndustries, Germany.

The electrolyte provides for ion transport between the anode and cathodeof the battery during the charge and discharge processes. We refer tosolutions comprising solvated ions as electrolytes, and ioniccompositions that dissolve to form solvated ions in appropriate liquidsare referred to as electrolyte salts. Electrolytes for lithium ionbatteries can comprise one or more selected lithium salts. Appropriatelithium salts generally have inert anions. Suitable lithium saltsinclude, for example, lithium hexafluorophosphate, lithiumhexafluoroarsenate, lithium bis(trifluoromethyl sulfonyl imide), lithiumtrifluoromethane sulfonate, lithium tris(trifluoromethyl sulfonyl)methide, lithium tetrafluoroborate, lithium perchlorate, lithiumtetrachloroaluminate, lithium chloride, lithium difluoro oxalato borate,and combinations thereof. In some embodiments, the electrolyte comprisesa 1 M concentration of the lithium salts, although greater or lesserconcentrations can be used.

For lithium ion batteries of interest, a non-aqueous liquid is generallyused to dissolve the lithium salt(s). The solvent generally does notdissolve the electroactive materials. Appropriate solvents include, forexample, propylene carbonate, dimethyl carbonate, diethyl carbonate,2-methyl tetrahydrofuran, dioxolane, tetrahydrofuran, methyl ethylcarbonate, γ-butyrolactone, dimethyl sulfoxide, acetonitrile, formamide,dimethyl formamide, triglyme (tri(ethylene glycol)dimethyl ether),diglyme (diethylene glycol dimethyl ether), DME (glyme or1,2-dimethyloxyethane or ethylene glycol dimethyl ether), nitromethaneand mixtures thereof. Particularly useful solvents for high voltagelithium-ion batteries are described further in copending U.S. patentapplications 2011/0136019 to Amiruddin et al. entitled: “Lithium ionbattery with high voltage electrolytes and additives”, incorporatedherein by reference.

Electrolyte with fluorinated additives has shown to further improve thebattery performance for batteries with silicon based negative electrodeactive material. The fluorinated additives can include, for example,fluoroethylene carbonate, fluorinated vinyl carbonate, monochloroethylene carbonate, monobromo ethylene carbonate,4-(2,2,3,3-tetrafluoropropoxymethyl)-[1,3]dioxolan-2-one,4-(2,3,3,3-tetrafluoro-2-trifluoro methyl-propyl)-[1,3]dioxolan-2-one,4-trifluoromethyl-1,3-dioxolan-2-one, bis(2,2,3,3-tetrafluoro-propyl)carbonate, bis(2,2,3,3,3-pentafluoro-propyl) carbonate, or mixturesthereof. In some embodiments, the electrolyte can comprise from about 1weight percent to about 35 weight percent halogenated carbonate, infurther embodiments from about 3 weight percent to about 30 weightpercent and in other embodiments from about 5 weight percent to about 20weight percent halogenated carbonate in the electrolyte as a fraction ofthe solvent plus electrolyte salt, as a fraction of the totalelectrolyte weight. A person of ordinary skill in the art will recognizethat additional ranges of halogenated carbonate concentrations withinthe explicit ranges above are contemplated and are within the presentdisclosure. As described further in the Examples below, theincorporation of halogenated carbonate into the electrolyte has beenobserved to significantly improve the specific capacity and the cyclingproperties of batteries. Also, electrolytes with fluoroethylenecarbonate have been found to have excellent low temperature performanceas described in copending U.S. patent application Ser. No. 13/325,367 toLi et al. (the '367 application), now published application US2013/0157147, entitled “Low Temperature Electrolyte for High CapacityLithium Based Batteries,” incorporated herein by reference.

The battery described herein can be assembled into various commercialbattery designs such as prismatic shaped batteries, wound cylindricalbatteries, coin cell batteries, or other reasonable battery shapes. Thebatteries can comprise a single pair of electrodes or a plurality ofpairs of electrodes assembled in parallel and/or series electricalconnection(s). While the materials described herein can be used inbatteries for primary, or single charge use, the resulting batteriesgenerally have desirable cycling properties for secondary battery useover multiple cycling of the batteries.

In some embodiments, the positive electrode and negative electrode canbe stacked with the separator between them, and the resulting stackedstructure can be rolled into a cylindrical or prismatic configuration toform the battery structure. Appropriate electrically conductive tabs canbe welded or the like to the current collectors, and the resultingjellyroll structure can be placed into a metal canister or polymerpackage, with the negative tab and positive tab welded to appropriateexternal contacts. Electrolyte is added to the canister, and thecanister is sealed to complete the battery. Some presently usedrechargeable commercial batteries include, for example, the cylindrical18650 batteries (18 mm in diameter and 65 mm long) and 26700 batteries(26 mm in diameter and 70 mm long), although other battery sizes can beused, as well as prismatic cells and foil pouch batteries of selectedsizes.

Pouch cell batteries can be particularly desirable for vehicleapplications due to stacking convenience and relatively low containerweight. A desirable pouch battery design for vehicle batteriesincorporating a high capacity cathode active materials is described indetail in published U.S. patent applications 2009/0263707 to Buckley etal, entitled “High Energy Lithium Ion Secondary Batteries” and2012/0028105 to Kumar et al. (the '105 application), entitled “BatteryPacks for Vehicles and High Capacity Pouch Secondary Batteries forIncorporation into Compact Battery Packs,” both incorporated herein byreference. While the pouch battery designs are particularly convenientfor use in specific battery pack designs, the pouch batteries can beused effectively in other contexts as well with high capacity in aconvenient format. In one embodiment, the pouch cell batteries describedherein uses a ceramic type of separator to improve cycling stability andsafety of the battery.

A representative embodiment of a pouch battery is shown in FIGS. 2( a)to 2(c). In this embodiment, pouch battery 160 comprises pouch enclosure162, battery core 164 and pouch cover 166. Pouch enclosure 162 comprisesa cavity 170 and edge 172 surrounding the cavity. Cavity 170 hasdimensions such that battery core 164 can fit within cavity 170. Pouchcover 166 can seal around edge 172 to seal battery core 164 within thescaled battery, as shown in FIGS. 2( b) and 2(c). Referring to FIG. 2(b), the pouch enclosure 162 is sealed with the pouch cover 166 alongedge 172 to form the pouch battery 160. Terminal tabs 174, 176 extendoutward from the sealed pouch for electrical contact with battery core164. FIG. 2( c) is a schematic diagram of a cross section of the batteryof FIG. 2( b) viewed along the A-A line. Specifically, battery core 164is shown to be encased inside the cavity 170 of the pouch enclosure 162sealed along the edge 172 with pouch cover 166 to form the pouch battery160. Many additional embodiments of pouch batteries are possible withdifferent configurations of the edges and seals.

In general, the number of layers can be selected depending on theloading levels of the cathode (positive electrode) and anode (negativeelectrode). For a specific energy density, a battery with a highercathode loading on the current collector with a respective balancedanode has a fewer number of layers relative to a battery with a cathodeof a lower loading level on the current collector. The number of layersof cathode can be selected in some embodiments between a value of 5 and30. In typical designs, the anode has one layer in excess of thecathode, e.g., 5 cathode layers and 6 anode layers. The number ofelectrode layer for a selected energy density also depends on the sizeof the electrodes. For electrodes with bigger areas, the number oflayers can be fewer compared with a battery with electrodes having asmaller area.

High Capacity Anode

In general, the battery designs herein are based on a high capacityanode active material. Specifically, the anode active materialsgenerally have a specific capacity of at least about 700 mAh/g, infurther embodiments at least about 800 mAh/g and in additionalembodiments at least about 900 mAh/g when cycled at a rate of C/10against lithium metal from 0.005V to 1.5V. As this implies, the specificcapacity of negative electrode active material can be evaluated in acell with a lithium metal counter electrode. However, in the batteriesdescribed herein, the negative electrodes can exhibit comparablespecific capacities when cycled against high capacity lithium metaloxide positive electrode active materials. In the battery withnon-lithium metal electrodes, the specific capacity of the respectiveelectrodes can be evaluated by dividing the battery capacity by therespective weights of the active materials.

New formulations of silicon based negative electrode active materialshave been developed with high capacity and reasonable cyclingproperties. Elemental silicon has attracted significant amount ofattention as a potential negative electrode material due to its veryhigh specific capacity with respect to intake and release of lithium.Silicon forms an alloy with lithium, which can theoretically have alithium content corresponding with more than 4 lithium atoms per siliconatom (e.g., Li_(4.4)Si). Thus, the theoretical specific capacity ofsilicon is on the order of 4000-4400 mAh/g, which is significantlylarger than the theoretical capacity of about 370 mAh/g for graphite.Graphite is believed to intercalate lithium to a level of roughly 1lithium atom for 6 carbon atoms (LiC₆). Also, elemental silicon, siliconalloys, silicon composites and the like can have a low potentialrelative to lithium metal similar to graphite. However, siliconundergoes a very large volume change upon alloying with lithium. A largevolume expansion on the order of two to four times of the originalvolume or greater has been observed, and the large volume changes havebeen correlated with a significant decrease in the cycling stability ofbatteries having silicon-based negative electrodes.

Germanium has a similar chemistry to silicon, and germanium andgermanium oxide can be used to alloy/intercalate lithium similarly tosilicon and silicon oxide as described below. Thus, germanium basedactive anode materials can be substituted for silicon based materialsdescribed herein, and generally similar composites, alloys and mixturesthereof can be formed with germanium as are described for silicon.Germanium has a theoretical specific capacity of 1623 mAh/g compared tothe silicon theoretical specific capacity of 4200 mAh/g. Similarly, tin(Sn), tin alloys and tin compounds can intercalate/alloy with lithiumwith a fairly high capacity and a desirable voltage range. Tin metal hasa theoretical specific capacity of 993 mAh/g with respect to lithiumalloying. Therefore, tin based active materials, such as tin, tin alloys(e.g., with Zn, Cd or In), tin oxides (SnO, Sn₂O₃ or Sn₃O₄), tincompounds (e.g., ZnSnO₄) or mixtures thereof, can be used as a highspecific capacity anode active material. In general, to achieve thedesired energy densities for the batteries, any high capacity anodematerial can be used having a specific capacity of at leastapproximately 700 mAh/g.

Also, elemental silicon as well as other high capacity materials in anegative electrode of a lithium-based battery can exhibit in someformulations a large irreversible capacity loss (IRCL) in the firstcharge/discharge cycle of the battery. The high IRCL of a silicon-basedanode can consume a significant portion of the capacity available forthe battery's energy output. Since the cathode, i.e., positiveelectrode, supplies all of the lithium in a traditional lithium ionbattery, a high IRCL in the anode, i.e., negative electrode, can resultin a low energy battery. In order to compensate for the large anodeIRCL, supplemental lithium can be added to the negative electrodematerial to offset the IRCL. The use of supplemental lithium to improvethe performance of silicon based electrodes is described also in the'294 application cited above, and Ser. No. 13/108,708 to Deng et al.(the '708 application), now published application 2012/0295155,entitled: “Silicon oxide based high capacity anode materials for lithiumion batteries”, both incorporated herein by reference. The use ofsupplemental lithium in the improved battery designs is describedfurther below.

High capacity silicon based anode undergoes volume expansion during thecharge/discharge process. To adapt to the volume expansion, the anode ofthe batteries described herein can use nanostructured active siliconbased materials to accommodate better for volume expansion and thusmaintain the mechanical electrode stability and cycle life of thebattery. Nanostructured silicon based negative electrode compositionsare disclosed in the '294 application, the '708 application, as well ascopending U.S. patent application Ser. No. 13/354,096 to Anguchamy etal. (the '096 application), now publishes application US 2013/0189575,entitled: “Porous silicon based anode material formed using metalreduction,” all incorporated herein by reference.

Suitable nanostructured silicon can include, for example, nanoporoussilicon and nanoparticulate silicon. Also, nanostructured silicon can beformed into composites with carbon and/or alloys with other metalelements. The objective for the design of improved silicon-basedmaterials is to further stabilize the negative electrode materials overcycling while maintaining a high specific capacity and in someembodiments reducing the irreversible capacity loss in the first chargeand discharge cycle. Furthermore, pyrolytic carbon coatings are alsoobserved to stabilize silicon-based materials with respect to batteryperformance.

Silicon nanoparticles can provide a high surface area material that candesirably adapt to volume changes in the material during silicon-lithiumalloying. In general, nanoparticle silicon can comprise amorphous and/orcrystalline silicon nanoparticles. Crystalline silicon nanoparticles canbe desirable in some embodiments because of their larger electricalconductivity, relative to amorphous silicon nanoparticles. As usedherein, nanoparticle silicon can comprise submicron particles with anaverage primary particle diameter of no more than about 500 nm, infurther embodiments no more than about 250 nm, and in additionalembodiments no more than about 200 nm. A particle diameter refers to theaverage diameters along principle axes of a particle. Primary particledimensions refer to the dimensions of the particulates visible in atransmission electron micrograph, and the primary particles may or maynot exhibit some degree of agglomeration and/or fusing. The primaryparticle size generally reflects the surface area of the particlecollection, which is a significant parameter for performance as abattery active material. The BET surface area can range from about 1m²/g to about 700 m²/g, and in further embodiments form about 5 m²/g toabout 500 m²/g. BET surface areas can be evaluated, for example, usingcommercially available instruments. A person of ordinary skill in theart will recognize that additional ranges of particle size and surfaceareas within the explicit ranges above are contemplated and are withinthe present disclosure.

Another suitable form of nanostructured silicon comprises porous siliconparticles with nanostructured pores, and negative electrode activematerial can desirably comprise porous silicon and/or compositesthereof. Porous silicon can have improved cycling behavior due to itshigh surface area and/or void volume, which can facilitate accommodationof volume changes with lithium alloying and de-alloying. In someembodiments, doped and non-doped porous silicon can be formed on bulksilicon by electrochemical etching of silicon wafers. Recent work hasdeveloped porous silicon with significantly improved battery performancethrough the reduction of silicon oxide, as described further below.

In some embodiments, the negative electrode active composition cancomprise a silicon-metal alloy and/or intermetallic material. Suitablesilicon-metal intermetallic alloys are described in published U.S.patent application 2009/0305131A to Kumar et al., entitled “High EnergyLithium Ion Batteries With Particular Negative electrode Compositions,”incorporated herein by reference. The alloy/intermetallic materials canbe represented by the formula Si_(x)Sn_(q)M_(y)C_(z) where (q+x)>2y+Z,q≧0, z≧0, and M is metal selected from manganese, molybdenum, niobium,tungsten, tantalum, iron, copper, titanium, vanadium, chromium, nickel,cobalt, zirconium, yttrium, and combinations thereof. See also,published U.S. patent application 2007/0148544A to Le, entitled“Silicon-Containing Alloys Useful as Electrodes for Lithium-IonBatteries,” incorporated herein by reference. In the materials describedherein, generally the carbon materials and processing conditions areselected such that the carbon does not form a composition with thesilicon. Results have been presented with alloys having z=0 and q=0, sothat the formula simplifies to Si_(x)M_(y), where x>2y and M=Fe or Cu.See the '294 application cited above. The alloys were formed byappropriate milling.

With respect to the composite materials, nanostructured siliconcomponents can be combined with, for example, carbon nanoparticlesand/or carbon nanofibers. The components can be, for example, milled toform the composite, in which the materials are intimately associated.Generally, it is believed that the association has a mechanicalcharacteristic, such as the softer silicon coated over or mechanicallyaffixed with the harder carbon materials. In additional or alternativeembodiments, the silicon can be milled with metal powders to formalloys, which may have a corresponding nanostructure. The carboncomponents can be combined with the silicon-metal alloys to formmulti-component composites.

Also, carbon coatings can be applied over the silicon-based materials toimprove electrical conductivity, and the carbon coatings seem to alsostabilize the silicon based material with respect to improving cyclingand decreasing irreversible capacity loss. Desirable carbon coatings canbe formed by pyrolizing organic compositions. The organic compositionscan be pyrolyzed at relatively high temperatures, e.g., about 800° C. toabout 900° C., to form a hard amorphous coating. In some embodiments,the desired organic compositions can be dissolved in a suitable solvent,such as water and/or volatile organic solvents for combining with thesilicon based component. The dispersion can be well mixed withsilicon-based composition. After drying the mixture to remove thesolvent, the dried mixture with the silicon based material coated withthe carbon precursor can be heated in an oxygen free atmosphere topyrolyze the organic composition, such as organic polymers, some lowermolecular solid organic compositions and the like, and to form a carboncoating, such as a hard carbon coating. The carbon coating can lead tosurprisingly significant improvement in the capacity of the resultingmaterial. Also, environmentally friendly organic compositions, such assugars and citric acid, have been found to be desirable precursors forthe formation of pyrolytic carbon coatings. Elemental metal coatings,such as silver or copper, can be applied as an alternative to apyrolytic carbon coating to provide electrical conductivity and tostabilize silicon-based active material. The elemental metal coatingscan be applied through solution based reduction of a metal salt.

In some embodiments, the negative electrode active material comprises acomposite of a carbon material and a silicon-based material. The siliconmaterial, the carbon material or both can be nanostructured, and thenanostructured components can then be combined to form a composite ofthe silicon component and the carbon component. For example, thecomponents of the composite can be milled together to form thecomposite, in which the constituent materials are intimately associated,but generally not alloyed. The nanostructures characteristics aregenerally expected to manifest themselves in the composite, althoughcharacterization of the composites may be less established relative tothe characterization of the component materials. Specifically, thecomposite material may have dimensions, porosity or other high surfacearea characteristics that are manifestations of the nano-scale of theinitial materials. In some embodiments, the negative electrode activematerial can comprise a silicon-based material coated onto a carbonnanofibers and/or carbon nanoparticles.

Porous Silicon (pSi) Based Material

Desirable high capacity negative electrode active materials can compriseporous silicon (pSi) based materials and/or composites of the poroussilicon based materials. In general, the pSi based material compriseshighly porous crystalline silicon that can provide high surface areasand/or high void volume relative to bulk silicon. While nanostructuredporous silicon can be formed through a variety of approaches such aselectrochemical etching of a silicon wafer, particularly good batteryperformance has been obtained from nanostructured porous siliconobtained by metal reduction of silicon oxide powders. In particular, thematerial has particularly good cycling properties while maintaining ahigh specific capacity. The formation of composites of pSi basedmaterial with carbon based material or metal can additionallymechanically stabilize the negative electrode for improved cycling.Additional description of the pSi based material from the reduction ofsilicon oxide can be found in copending '096 application referencedabove.

The porous silicon based material can be formed using metal reduction,which in some embodiments comprises gradual heating followed by acidetching to produce the pSi based material. The etching can be used toremove by-product metal oxide material, the removal of which cancontribute to the desired porosity. In some embodiments, the pSi basedmaterial generally is substantially free of elemental carbon within thenanostructured material. The nanostructured pSi can have surface areafrom about 10 m²/g to about 200 m²/g and in additional embodiments fromabout 10 m²/g to about 150 m²/g. A person of ordinary skill in the artwill recognize that additional ranges of values within the explicit BETsurface area ranges above are contemplated and are within the presentdisclosure. For a given particle size, the surface area of a porousmaterial can also relate to the pore sizes and void volumes.

While the pSi nanostructured material is substantially free of carbon,an electrode formed from the pSi based material can comprise a carboncomponent, such as a nano-scale carbon (e.g., nanotubes, fibers orparticles), graphitic carbon and/or a pyrolytic carbon coating toprovide an electrically conductive additive that is not intimatelymilled with the porous silicon. Desirable pyrolytic carbon coatings canbe formed from organic compositions that can be applied with a solventto obtain a relatively uniform coating prior to and after pyrolizing theorganic composition to form the carbon coating. An elemental metalcoating can be applied as an alternative to a carbon coating. When thenegative electrode is made from a porous silicon based material, theelectrode can have a first cycle C/20 charge capacity in the range ofabout 3000 mAh/g to about 3900 mAh/g and discharge capacity in the rangeof about 2400 mAh/g to about 2800 mAh/g, a C/3 discharge capacity in therange of about 1800 to about 2600 mAh/g, and an irreversible capacityloss of less than about 35%. The pSi based material can have specificcapacity of at least about 2000 mAh/g when cycled at C/3 rate. The pSibased materials can be effectively cycled with a high capacity lithiumrich positive electrode active material. The resulting lithium ionbatteries can have high specific capacities for both the negativeelectrode active material and the positive electrode active material.

Silicon Oxide Carbon (SiO-C) Based Composites

Silicon oxide based compositions have been formed into compositematerials with high capacities and very good cycling properties asdescribed in the '708 application referenced above. In particular,oxygen deficient silicon oxides can be formed into composites withelectrically conductive materials, such as conductive carbons or metalpowders, which surprisingly significantly improve cycling whileproviding for high values of specific capacity. Furthermore, the millingof the silicon oxides into smaller particles, such as submicronstructured materials, can further improve the performance of thematerials. The silicon oxide based materials maintain their highcapacities and good cycling as negative electrode active materials whenplaced into lithium ion batteries with high capacity lithium metal oxidepositive electrode active materials. The cycling can be further improvedwith the addition of supplemental lithium into the battery and/or withan adjustment of the balance of the active materials in the respectiveelectrodes. Supplemental lithium can replace at least some of thelithium lost to the irreversible capacity loss due to the negativeelectrode and can stabilize the positive electrode with respect tocycling. When configured with high capacity lithium rich manganeseoxides based positive electrodes, the silicon oxide based electrode canexhibit excellent cycling at reasonable rates. Based on appropriatedesigns of the batteries, high energy density batteries can be produced,and the batteries are suitable for a range of commercial applications.

As with silicon, oxygen deficient silicon oxide, e.g., silicon oxide,SiO_(x), 0.1≦x≦1.9, can intercalate/alloy with lithium such that theoxygen deficient silicon oxide can perform as an active material in alithium ion battery. These oxygen deficient silicon oxide materials aregenerally referred to as silicon oxide based materials and in someembodiments can contain various amounts of silicon, silicon oxide, andsilicon dioxide. The oxygen deficient silicon oxide can incorporate arelatively large amount of lithium such that the material can exhibit alarge specific capacity. However, silicon oxide is observed generally tohave a capacity that fades quickly with battery cycling, as is observedwith elemental silicon. The silicon oxides can be made into compositematerials to address the cycling fade of the silicon oxide basedmaterials. For example, composites can be formed with electricallyconductive components that contribute to the conductivity of theelectrode as well as the stabilization of the silicon oxide duringcycling.

Silicon oxide based materials with greater capacity upon cycling can beproduced through the milling of the silicon oxide to form smallerparticles. Additionally, the silicon oxide based materials can be formedinto composites with electrically conductive powders in combination withhigh energy mechanical milling (HEMM) or the like. Alternatively oradditionally, the silicon oxide based materials can be subjected to hightemperature heat treatment. Smaller silicon oxide particles obtainedfrom HEMM treatment has shown greater capacity in either silicon oxideelectrode or electrodes with composites of silicon oxide-conductivecarbon particle, e.g., graphitic carbon, than commercial silicon oxideswith larger particle sizes. Pyrolytic carbon coated silicon oxidecomposites showed improved conductivity and specific capacity. Siliconoxide composites with inert metal particles with or without a pyrolyticcarbon coating have shown very good cycling performance at high specificcapacity. Suitable inert metal particles are described further below.The milling of the silicon oxide based materials with metal powdersseems to reduce the introduction of inert material from the grindingmedium, e.g., zirconium oxide, into the product composite. Composites ofsilicon oxide, graphite, and pyrolytic carbon in particular have shownsignificantly improved specific capacity and cycling performance.

HEMM and/or heat treatment under appropriate conditions can result insome disproportionation of oxygen deficient silicon oxides into SiO₂ andelemental Si. Small crystalline silicon peaks are observed under someprocessing conditions. It is possible that the processed materials havesome components of amorphous elemental silicon and/or small crystalliteswithin the structure. However, it is believed that most of the siliconoxide based materials used herein have significant components of oxygendeficient silicon oxide and amounts of elemental silicon have not beenquantified. In some embodiments, elemental silicon powders, such assubmicron silicon particles, can be included in the formation ofcomposites with silicon oxide based materials.

In general, a range of composites are used and can comprise siliconoxide, carbon components, such as graphitic particles (Gr), inert metalpowders (M), elemental silicon (Si), especially nanoparticles, pyrolyticcarbon coatings (HC), carbon nano fibers (CNF), or combinations thereof.Thus, the general compositions of the composites can be represented asαSiO-βGr-χHC-δM-εCNF-φSi, where α, β, γ, δ, ε, and φ are relativeweights that can be selected such that α+β+γ+δ+ε+φ=1. Generally0.35<α<1, 0≦β<0.6, 0≦χ<0.65, 0≦δ<0.65, 0≦ε<0.65, and 0≦φ<0.65. Certainsubsets of these composite ranges are of particular interest. In someembodiments, composites with SiO and one or more carbon based componentsare desirable, which can be represented by a formula αSiO-βGr-χHC-εCNF,where 0.35<α<0.9, 0≦β<0.6, 0≦χ<0.65 and 0≦ε<0.65 (δ=0 and φ=0), infurther embodiments 0.35<α<0.8, 0.1≦β<0.6, 0.0≦χ<0.55 and 0≦ε<0.55, insome embodiments 0.35<α<0.8, 0≦β<0.45, 0.0≦χ<0.55 and 0.1≦ε<0.65, and inadditional embodiments 0.35<α<0.8, 0≦β<0.55, 0.1≦χ<0.65 and 0≦ε<0.55. Inadditional or alternative embodiments, composites with SiO, inert metalpowders and optionally one or more conductive carbon components can beformed that can be represented by the formula αSiO-βGr-χHC-δM-εCNF,where 0.35<α<1, 0≦β<0.55, 0≦χ<0.55, 0.1≦δ<0.65, and 0≦ε<0.55. In furtheradditional or alternative embodiments, composites of SiO with elementalsilicon and optionally one or more conductive carbon components can beformed that can be represented by the formula αSiO-βGr-χHC-εCNF-φSi,where 0.35<α<1, 0≦β<0.55, 0≦χ<0.55, 0≦ε<0.55, and 0.1≦φ<0.65 and infurther embodiments 0.35<α<1, 0≦β<0.45, 0.1≦χ<0.55, 0≦ε<0.45, and0.1≦φ<0.55. A person or ordinary skill in the art will recognize thatadditional ranges within the explicit ranges above are contemplated andare within the present disclosure. As used herein, the reference tocomposites implies application of significant combining forces, such asfrom HEMM milling, to intimately associate the materials, in contrastwith simple blending, which is not considered to form composites.

The association of conductive carbon with the silicon oxide activematerial can improve the performance of the silicon oxide material in alithium ion battery. Composites with electrically conductive materialsand silicon oxide active material described herein provide very goodcycling performance. A milling process can be used to incorporateelectrically conductive diluents to form an intimate composite throughthe milling process. Graphitic carbon, e.g., nanostructured conductivecarbon, carbon nanoparticles and/or carbon nanofibers, can provide agood electrically conductive medium for the formation of composites withsilicon oxide. High energy milling can generally be performed with ahard ceramic milling media, such as zirconium oxide particles. Millingcan result in the incorporation of some milling media into the productcomposite material. Since the milling media is electrically insulatingand electrochemically inert, it is desirable to keep the amount ofmilling media in the product composite material, after separation of thebulk quantities of milling beads, to a low or possibly undetectablelevel.

Pyrolytic carbon coatings are also observed to stabilize silicon oxidebased materials with respect to battery performance. In particular, thepyrolytic carbon coatings can be placed over the initially preparedcomposites to provide an additional electrically conductive component ofthe product material. The combination of the pyrolytic carbon with asilicon oxide-particulate conductor composite provides surprisinglyimproved performance in some embodiments. The formation of pyrolyticcarbon coatings is described further above. In further embodiments,elemental metal coatings, such as silver or copper, can be applied as analternative to a pyrolytic carbon coating to provide electricalconductivity and to stabilize silicon oxide based active material. Theelemental metal coatings can be applied through solution based reductionof a metal salt.

In additional or alternative embodiments, the silicon oxide can bemilled with metal powders, in which the silicon oxide is milled to asmaller particle size and the metal is intimately combined with thesilicon oxide material to form a composite material, for example with ananostructure. The carbon components can be combined with thesilicon-metal alloys to form multi-component composites. The compositematerials with intimately combined components are distinguishable fromsimple blends of components held together with a polymer binder, whichlacks mechanical and/or chemical interactions to form a single compositematerial.

The capacity of the anode significantly governs the energy density ofthe battery. The higher the capacity of the anode material the lower isthe weight of the anode in the battery. When the negative electrode ismade from a silicon based material, the electrode can have a dischargespecific capacity at a rate of C/3 from about 800 mAh/g to 2500 mAh/g,in further embodiments from about 900 mAh/g to about 2300 mAh/g and inother embodiments from about 950 mAh/g to about 2200 mAh/g at C/3discharge from 1.5V to 5 mV against lithium metal. A person of ordinaryskill in the art will recognize that additional ranges of dischargespecific capacity within the explicit ranges above are contemplated andare within the present disclosure.

High Capacity Cathode

In general, positive electrode (cathode) active materials of interestcomprise a lithium intercalation material such as lithium metal oxidesor lithium metal phosphates. Positive electrode active materialsinclude, for example, as stoichiometric layered cathode materials withhexagonal lattice settings like LiCoO₂, LiNiO₂,LiCo_(1/3)Mn_(1/3)Ni_(1/3)O₂ or the like; cubic spinel cathode materialssuch as LiMn₂O₄, Li₄Mn₅O₁₂, or the like; olivine materials, such asLiMPO₄ (M=Fe, Co, Mn, combinations thereof and the like). Lithium richpositive electrode active materials are of interest due to their highcapacity, such as layered cathode materials, e.g.,Li_(1+x)(NiCoMn)_(0.33−x)O₂ (0≦x<0.3) systems; layer-layer composites,e.g., xLi₂MnO₃.(1−x)LiMO₂ where M can be Ni, Co, Mn, combinationsthereof and the like; and composite structures like layered-spinelstructures such as LiMn₂O₄.LiMO₂. In some embodiments, a lithium richcomposition can be referenced relative to a composition LiMO₂, where Mis one or more metals with an average oxidation state of +3.

Generally, the lithium rich compositions can be representedapproximately with a formula Li_(1+x)M_(1−y)O₂, where M represents oneor more non-lithium metals and y is related to x based on the averagevalance of the metals. In layered-layered composite compositions, x isapproximately equal to y. The additional lithium in the initial cathodematerial can provide to some degree corresponding additional activelithium for cycling that can increase the battery capacity for a givenweight of cathode active material. In some embodiments, the additionallithium is accessed at higher voltages such that the initial chargetakes place at a higher voltage to access the additional capacity.

Lithium rich positive electrode active materials of particular interestare represented approximately by a formula

Li_(1+b)Ni_(α)Mn_(β)Co_(γ)A_(δ)O_(2−z)F_(z)  Formula I

where b ranges from about 0.05 to about 0.3, α ranges from about 0 toabout 0.4, β ranges from about 0.2 to about 0.65, γ ranges from 0 toabout 0.46, δ ranges from 0 to about 0.15 and z ranges from 0 to about0.2 with the proviso that both α and γ are not zero, and where A is ametal element different from Ni, Mn, Co, or a combination thereof.Element A and F (fluorine) are optional cation and anion dopants,respectively. Element A can be, for example Mg, Sr, Ba, Cd, Zn, Al, Ga,B, Zr, Ti, Ca, Ce, Y, Nb, Cr, Fe, V, Li or combinations thereof. Aperson of ordinary skill in the art will recognize that additionalranges of parameter values within the explicit compositional rangesabove are contemplated and are within the present disclosure. Tosimplify the following discussion in this section, the optional dopantsare not discussed further.

The formulas presented herein for the positive electrode activematerials are based on the molar quantities of starting materials in thesynthesis, which can be accurately determined. With respect to themultiple metal cations, these are generally believed to bequantitatively incorporated into the final material with no knownsignificant pathway resulting in the loss of the metals from the productcompositions. Of course, many of the metals have multiple oxidationstates, which are related to their activity with respect to thebatteries. Due to the presence of the multiple oxidation states andmultiple metals, the precise stoichiometry with respect to oxygengenerally is only roughly estimated based on the crystal structure,electrochemical performance and proportions of reactant metals, as isconventional in the art. However, based on the crystal structure, theoverall stoichiometry with respect to the oxygen is reasonablyestimated. All of the protocols discussed in this paragraph and relatedissues herein are routine in the art and are the long establishedapproaches with respect to these issues in the field.

The stoichiometric selection for the compositions can be based on somepresumed relationships of the oxidation states of the metal ions in thecomposition. As an initial matter, if in Formula I above, b+α+β+γ+δ isapproximately equal to 1, then the composition can be correspondinglyapproximately represented by a two component notation as:

xLi₂M′O₃.(1−x)LiMO₂  Formula II

where 0<x<1, M is one or more metal cations with an average valance of+3 with at least one cation being a Mn ion or a Ni ion and where M′ isone or more metal cations with an average valance of +4. It is believedthat the layered-layered composite crystal structure has a structurewith the excess lithium supporting the formation of an alternativecrystalline phase. For example, in some embodiments of lithium richmaterials, a Li₂MnO₃ material may be structurally integrated with eithera layered LiMO₂ component where M represents selected non-lithium metalelements or combinations thereof. These compositions are describedgenerally, for example, in U.S. Pat. No. 6,680,143 to Thackeray et al.,entitled “Lithium Metal Oxide Electrodes for Lithium Cells andBatteries,” which is incorporated herein by reference.

Recently, it has been found that the performance properties of thepositive electrode active materials can be engineered around thespecific design of the composition stoichiometry. The positive electrodeactive materials of particular interest can be represented approximatelyin two component notation as:

xLi₂MnO₃.(1−x)LiMO₂  Formula III

where M is one or more metal elements with an average valance of +3 andwith one of the metal elements being Mn and with another metal elementbeing Ni and/or Co. In general, in Formula II and III above, the x is inthe range of 0<x<1, but in some embodiments 0.03≦x≦0.6, in furtherembodiments 0.075≦x≦0.50, in additional embodiments 0.1≦x≦0.45, and inother embodiments 0.15≦x≦0.425. A person of ordinary skill in the artwill recognize that additional ranges within the explicit ranges ofparameter x above are contemplated and are within the presentdisclosure.

In some embodiments, M in Formula III comprises manganese, nickel,cobalt or a combination thereof along with an optional dopant metal andcan be written as Ni_(u)Mn_(v)Co_(w)A_(y), where A is a metal other thanNi, Mn or Co. Consequently Formula III now becomes:

x.Li₂MnO₃.(1−x)LiNi_(u)Mn_(v)Co_(w)A_(y)O₂  Formula IV

where u+v+w+y≈1. While Mn, Co and Ni have multiple accessible oxidationstates, which directly relates to their use in the active material, inthese composite materials if appropriate amounts of these elements arepresent, it is thought that the elements can have the oxidation statesMn⁺⁴, Co⁺³ and Ni⁺². In the overall formula, the total amount ofmanganese has contributions from both constituents listed in the twocomponent notation. Additionally, if δ=0 in Formula I, the two componentnotation of Formula IV can simplify with v≈u tox.Li₂MnO₃.(1−x)LiNi_(u)Mn_(u)Co_(w)O₂, with 2u+w=1.

In some embodiments, the stoichiometric selection of the metal elementscan be based on the above presumed oxidation states. Based on theoxidation state of dopant element A, corresponding modifications of theformula can be made. Also, compositions can be considered in which thecomposition varies around the stoichiometry with v≈u. The engineering ofthe composition to obtain desired battery performance properties isdescribed further in copending U.S. patent application 2011/0052981 (the'981 application) to Lopez et al., entitled “Layer-Layer Lithium RichComplex Metal Oxides With High Specific Capacity and Excellent Cycling,”incorporated herein by reference. Similar compositions have beendescribed in published U.S. patent application 2010/0086853A (the '853application) to Venkatachalam et al. entitled “Positive ElectrodeMaterial for Lithium Ion Batteries Having a High Specific DischargeCapacity and Processes for the Synthesis of these Materials”, andpublished U.S. patent application 2010/0151332A (the '332 application)to Lopez et al. entitled “Positive Electrode Materials for HighDischarge Capacity Lithium Ion Batteries”, both incorporated herein byreference.

The positive electrode material can be advantageously synthesized byco-precipitation and sol-gel processes detailed in the '853 applicationand the '332 application. In some embodiments, the positive electrodematerial is synthesized by precipitating a mixed metal hydroxide orcarbonate composition from a solution comprising +2 cations wherein thehydroxide or carbonate composition has a selected composition. The metalhydroxide or carbonate precipitates are then subjected to one or moreheat treatments to form a crystalline layered lithium metal oxidecomposition. A carbonate co-precipitation process described in the '332application gave desired lithium rich metal oxide materials havingcobalt in the composition and exhibiting the high specific capacityperformance with superior tap density. These copending patentapplications also describe the effective use of metal fluoride coatingsto improve performance and cycling.

It is found that for many positive electrode active materials a coatingon the material can improve the performance of the resulting batteries.Suitable coating materials, which are generally believed to beelectrochemically inert during battery cycling, can comprise metalfluorides, metal oxides, metal non-fluoride halides or metal phosphates.The results in the Examples below are obtained with materials coatedwith metal fluorides.

For example, the general use of metal fluoride compositions as coatingsfor cathode active materials, specifically LiCoO₂ and LiMn₂O₄, isdescribed in published PCT application WO 2006/109930A to Sun et al.,entitled “Cathode Active Material Coated with Fluorine Compound forLithium Secondary Batteries and Method for Preparing the Same,”incorporated herein by reference. Improved metal fluoride coatings withappropriately engineered thicknesses are described in copending U.S.patent application 2011/0111298 to Lopez et al, (the '298 application)entitled “Coated Positive Electrode Materials for Lithium IonBatteries,” incorporated herein by reference. Suitable metal oxidecoatings are described further, for example, in copending U.S. patentapplication 2011/0076556 to Karthikeyan et al. entitled “Metal OxideCoated Positive Electrode Materials for Lithium-Based Batteries”,incorporated herein by reference. The discovery of non-fluoride metalhalides as desirable coatings for cathode active materials is describedin published U.S. patent application serial number 2012/0070725 toVenkatachalam et al., entitled “Metal Halide Coatings on Lithium IonBattery Positive Electrode Materials and Corresponding Batteries,”incorporated herein by reference. The synthesis approaches along withthe coating provide for superior performance of the materials withrespect to capacity as well as cycling properties. The desirableproperties of the active material along with the use of desirable anodematerial described herein provide for improved battery performance.

In some embodiments, the positive electrode active material has aspecific capacity during the tenth cycle at a discharge rate of C/3 ofat least about 180 milliamp hours per gram (mAh/g), in additionalembodiments from about 200 mAh/g to about 310 mAh/g, in furtherembodiments from about 215 mAh/g to about 300 mAh/g and in otherembodiment from about 225 mAh/g to about 290 mAh/g. Additionally, the20^(th) cycle discharge capacity of the material is at least about 98%,and in further embodiments 98.5% of the 5^(th) cycle discharge capacity,cycled at a discharge rate of C/3. Also, in some embodiments, thepositive electrode active material can have a first cycle chargecapacity from the open circuit voltage to 4.6 of about 250 mAh/g toabout 320 mAh/g at a rate of C/10 and a discharge capacity from 4.6V to2V from about 230 mAh/g to about 290 mAh/g at a rate of C/10. It hasbeen found that the first cycle irreversible capacity loss for inertcoated electroactive materials, e.g., coated with a metal halide or ametal oxide, can be decreased at least about 25%, and in furtherembodiments from about 30% to about 60% relative to the equivalentperformance of the uncoated materials. The tap density of a positiveelectrode active material described herein can be measured by usinggraduated measuring cylinders on a commercially available tap machinewith pre-determined tapping parameters. The tap density of the materialcan be at least about 1.8 g/mL, in further embodiments at least about1.9 g/mL and in additional embodiments from about 1.95 to about 2.75g/mL. High tap density translates into high overall capacity of abattery given a fixed volume. A person of ordinary skill in the art willrecognize that additional ranges of specific capacity and tap densityand of decreases in irreversible capacity loss are contemplated and arewithin the present disclosure. For fixed volume applications such asbatteries for electronic devices, high tap density therefore highoverall capacity of the battery is of particular significance.

Generally, tap density is the apparent powder density obtained understated conditions of tapping. The apparent density of a powder dependson how closely individual particles of the powder are pack together. Theapparent density is affected not only by the true density of the solids,but by the particle size distribution, particle shape and cohesiveness.Handling or vibration of powdered material can overcome some of thecohesive forces and allow particles to move relative to one another sosmaller particles can work their way into the spaces between the largerparticles. Consequently, the total volume occupied by the powderdecreases and its density increases. Ultimately no further naturalparticle packing can be measured without the addition of pressure and anupper limit of particle packing has been achieved. While electrodes areformed with the addition of pressure, a reasonably amount of pressure isonly effective to form a certain packing density of the electroactivematerials in the battery electrode. The actual density in the electrodegenerally relates to the tap density measured for a powder so that thetap density measurements are predictive of the packing density in abattery electrode with a higher tap density corresponding to a higherpacking density in the battery electrode.

The synthesis approaches for the high capacity positive electrode activematerials summarized above have been shown to be suitable to formmaterials with a high tap density. This is described further in the '332application cited above. As a result of a relatively high tap densityand excellent cycling performance, a battery can exhibit a high totalcapacity when the active material is incorporated into the cathode.Generally, a higher tap density can be advantageously used to obtain ahigh electrode density without sacrificing the performance of thematerial if the high tap density material has desirable performance.

Supplemental Lithium

The improved high energy battery designs described herein may or may notinclude supplemental lithium, and this section is directed to approachesfor the incorporation of supplemental lithium for appropriateembodiments. Various approaches can be used for the introduction ofsupplemental lithium into the battery, although following correspondinginitial reactions and/or charging, the negative electrode becomesassociated with excess lithium for cycling from the supplementallithium. With respect to the negative electrode in batteries havingsupplemental lithium, the structure and/or composition of the negativeelectrode can change relative to its initial structure and compositionfollowing the first cycle as well as following additional cycling.Depending on the approach for the introduction of the supplementallithium, the positive electrode may initially comprise a source ofsupplemental lithium and/or a sacrificial electrode can be introducedcomprising supplemental lithium. Additionally or alternatively,supplemental lithium can be associated with the negative electrode. Insome embodiments, the supplemental lithium can be introduced into thenegative electrode using electrochemical methods in contrast with purelychemical or mechanical methods. Chemical methods or mechanical methods,such as milling, may lead to effectively irreversible formation oflithium silicate, while the electrochemical method does not seem toresult in lithium silicate formation. In particular, the electrochemicalintroduction of lithium in general results in reversible lithiumincorporation, although lithium can be consumed in an initial formationof a solid electrolyte interphase (SEI) layer. With respect to initialstructure of the negative electrode, in some embodiments, the negativeelectrode has no changes due to the supplemental lithium. In particular,if the supplemental lithium is initially located in the positiveelectrode or a separate electrode, the negative electrode can be anunaltered form with no lithium present until the battery is charged orat least until the circuit is closed between the negative electrode andthe electrode with the supplemental lithium in the presence ofelectrolyte and a separator. For example, the positive electrode orsupplemental electrode can comprise elemental lithium, lithium alloyand/or other sacrificial lithium source.

If sacrificial lithium is included in the positive electrode, thelithium from the sacrificial lithium source is loaded into the negativeelectrode during the charge reaction. The voltage during the chargingbased on the sacrificial lithium source may be significantly differentthan the voltage when the charging is performed based on the positiveelectrode active material. For example, elemental lithium in thepositive electrode can charge the negative electrode active materialwithout application of an external voltage since oxidation of theelemental lithium drives the reaction. For some sacrificial lithiumsource materials, an external voltage is applied to oxidize thesacrificial lithium source in the positive electrode and drive lithiuminto the negative electrode active material. The charging generally canbe performed using a constant current, a stepwise constant voltagecharge or other convenient charging scheme. However, at the end of thecharging process, the battery should be charged to a desired voltage,such as 4.5V.

In further embodiments, at least a portion of the supplemental lithiumis initially associated with the negative electrode. For example, thesupplemental lithium can be in the form of elemental lithium, a lithiumalloy or other lithium source that is more electronegative than thenegative electrode active material. After the negative electrode is incontact with electrolyte, a reaction can take place, and thesupplemental lithium is transferred to the negative electrode activematerial. During this process, the solid electrolyte interface (SEI)layer is also formed. Thus, the supplemental lithium is loaded into thenegative electrode active material with at least a portion consumed information of the SEI layer. The excess lithium released from the lithiumrich positive electrode active material is also deposited into thenegative electrode active material during eventual charging of thebattery. The supplemental lithium placed into the negative electrodeshould be more electronegative than the active material in the negativeelectrode since there is no way of reacting the supplemental lithiumsource with the active material in the same electrode through theapplication of a voltage.

In some embodiments, supplemental lithium associated with the negativeelectrode can be incorporated as a powder within the negative electrode.Specifically, the negative electrode can comprise an active negativeelectrode composition and a supplemental lithium source within a polymerbinder matrix, and any electrically conductive powder if present. Inadditional or alternative embodiments, the supplemental lithium isplaced along the surface of the electrode. For example, the negativeelectrode can comprise an active layer with an active negative electrodecomposition and a supplemental lithium source layer on the surface ofactive layer. The supplemental lithium source layer can comprise a foilsheet of lithium or lithium alloy, supplemental lithium powder within apolymer binder and/or particles of supplemental lithium source materialembedded on the surface of the active layer. In an alternativeconfiguration, a supplemental lithium source layer is between the activelayer and current collector. Also, in some embodiments, the negativeelectrode can comprise supplemental lithium source layers on bothsurfaces of the active layer.

In additional embodiments, at least a portion of the supplementallithium can be supplied to the negative electrode active material priorto assembly of the battery. In other words, the negative electrode cancomprise partially lithium-loaded silicon based active material, inwhich the partially loaded active material has a selected degree ofloading of lithium through intercalation/alloying or the like. Forexample, for the preloading of the negative electrode active material,the negative electrode active material can be contacted with electrolyteand a lithium source, such as elemental lithium, lithium alloy or othersacrificial lithium source that is more electronegative than thenegative electrode active material.

An arrangement to perform such a preloading of lithium can comprise anelectrode with silicon-based active material formed on a currentcollector, which are placed in vessel containing electrolyte and a sheetof lithium source material contacting the electrode. The sheet oflithium source material can comprise lithium foil, lithium alloy foil ora lithium source material in a polymer binder optionally along with anelectrically conductive powder, which is in direct contact with thenegative electrode to be preloaded with lithium such that electrons canflow between the materials to maintain electrical neutrality while therespective reactions take place. In the ensuing reaction, lithium isloaded into the silicon based active material through intercalation,alloying or the like. In alternative or additional embodiments, thenegative electrode active material can be mixed in the electrolyte andthe lithium source material for incorporation of the supplementallithium prior to formation into an electrode with a polymer binder sothat the respective materials can react in the electrolytespontaneously.

In some embodiments, the lithium source within an electrode can beassembled into a cell with the electrode to be preloaded with lithium. Aseparator can be placed between the respective electrodes. Current canbe allowed to flow between the electrodes. Depending on the compositionof the lithium source it may or may not be necessary to apply a voltageto drive the lithium deposition within the silicon-based activematerial. An apparatus to perform this lithiation process can comprise acontainer holding electrolyte and a cell, which comprises an electrode,to be used as a negative electrode in an ultimate battery, a currentcollector, a separator and a sacrificial electrode that comprises thelithium source, where the separator is between the sacrificial electrodeand the electrode with the silicon-based active material. A convenientsacrificial electrode can comprise lithium foil, lithium powder embeddedin a polymer or lithium alloys, although any electrode with extractablelithium can be used. The container for the lithiation cell can comprisea conventional battery housing, a beaker, or any other convenientstructure. This configuration provides the advantage of being able tomeasure the current flow to meter the degree of lithiation of thenegative electrode. Furthermore, the negative electrode can be cycledonce or more than once in which the negative electrode active materialis loaded close to full loading with lithium. In this way, an SEI layercan be formed with a desired degree of control during the preloadingwith lithium of the negative electrode active material. Then, thenegative electrode is fully formed during the preparation of thenegative electrode with a selected preloading with lithium.

In general, the lithium source can comprise, for example, elementallithium, a lithium alloy or a lithium composition, such as a lithiummetal oxide, that can release lithium from the composition. Elementallithium can be in the form of a thin film, such as formed byevaporation, sputtering or ablation, a lithium or lithium alloy foiland/or a powder. Elemental lithium, especially in powder form, can becoated to stabilize the lithium for handling purposes, and commerciallithium powders, such as powders from FMC Corporation, are sold withproprietary coatings for stability. The coatings generally do not alterthe performance of the lithium powders for electrochemical applications.Lithium alloys include, for example, lithium silicon alloys and thelike. Lithium composition with intercalated lithium can be used in someembodiments, and suitable compositions include, for example, lithiumtitanium oxide, lithium tin oxide, lithium cobalt oxide, lithiummanganese oxide, and the like.

In general, for embodiments in which supplemental lithium is used, theamount of supplemental lithium preloaded or available to load into theactive composition can be in an amount of at least about 2.5% ofcapacity, in further embodiments from about 3 percent to about 40percent of capacity, in additional embodiments from about 5 percent toabout 35 percent of capacity, and in some embodiments from about 5percent to about 30 percent of the negative electrode active materialcapacity. The supplemental lithium can be selected to approximatelybalance the IRCL of the negative electrode, although other amounts ofsupplemental lithium can be used as desired. In some embodiment, thesupplemental lithium added is in an amount with an oxidation capacitycorresponding to from 0% to 120% of the IRCL of the negative electrode,in further embodiments, it is from 10% to 110%, and in other embodimentsfrom 20% to 100%. A person of ordinary skill in the art will recognizethat additional ranges of percentage within the explicit ranges aboveare contemplated and are within the present disclosure. Thus, thecontribution to the IRCL of the negative electrode can be effectivelyreduced or removed due to the addition of the supplemental lithium suchthat the measured IRCL of the battery represents partially or mostlycontributions from the IRCL of the positive electrode, which is notdiminished due to the presence of supplemental lithium. In someembodiments, the IRCL can be reduced to no more than about 20% of theinitial negative electrode capacity, in further embodiments no more thanabout 15%, in additional embodiments no more than about 10%. A person ofordinary skill in the art will recognize that additional ranges of IRCLwithin the explicit ranges above are contemplated and are within thepresent disclosure.

Balance of Cathode and Anode

The overall performance of the battery has been found to depend on thecapacities of both the negative electrode and positive electrode andtheir relative balance. Balance of the electrodes has been found to beextremely important with respect to achieving a high energy density forthe battery as well as to achieve good cycling properties. Whenassembling a battery, the anode and cathode capacities can beappropriately balanced to achieve good cycling performance during thecharge-discharge process due to the properties of the high capacitypositive electrode active materials. In some embodiments, high batteryenergy densities can be achieved through an effective under balancing ofthe negative electrode at low rates so that lithium metal plates ontothe negative electrode. In general, the plating of lithium metal on thenegative electrode is considered detrimental to cycling. But it has beenfound that the positive electrode capacity decreases a significantlygreater amount at high rates than the negative electrode for the highcapacity materials described herein. The different rate behavior of theelectrodes can be used advantageously in combination with cycling over afraction of the total depth of discharge. Specifically, an amount oflithium metal plating on the negative electrode at low rate can beeffectively stored on the positive electrode at high rate and/or areduced depth of discharge so that lithium metal no longer plates andless negative electrode capacity is wasted during cycling so that alower battery weight and volume can be achieved without sacrificingbattery capacity or cycling performance.

The positive electrode active material capacity can be estimated fromthe capacity of the material which can be measured by cycling thematerial against lithium metal foil. For example, for a given positiveelectrode, the capacity can be evaluated by determining the insertionand extraction capacities during the first charge/discharge cycle, wherethe lithium is de-intercalated or extracted from the positive electrodeto 4.6V and intercalated or inserted back into the positive electrode to2V at a rate of C/20. Similarly, for a given silicon based electrode,the insertion and extraction capacities can be evaluated with a batteryhaving a positive electrode comprising the silicon based active materialand a lithium foil negative electrode. The capacity is evaluated bydetermining the insertion and extraction capacities of the batteryduring the first charge/discharge cycle where lithium isintercalated/alloyed to the silicon based electrode to 5 mV andde-intercalated/de-alloyed to 1.5V at a rate of C/20.

In most commercially available carbon based batteries, approximately7-10% excess anode is taken over the cathode to prevent lithium plating.One important concern of too much excess anode is that the weight of thecell will increase reducing the energy density of the cell. Compared tographite which has a first cycle IRCL of ˜7%, high capacity siliconbased anodes can have IRCL ranging from about 10% to about 40%. A majorportion of the capacity becomes inactive in the cell after the firstcharge-discharge cycle and add to significant dead weight to thebattery. However, it has been found that properties of the electrodescan be advantageously used to balance the electrodes for realisticcycling conditions using a balance that is generally inappropriate forlow rate cycling.

For high capacity anode materials, the negative electrode irreversiblecapacity loss generally is greater than the positive electrodeirreversible capacity loss. If the negative electrode has asignificantly higher irreversible capacity loss than the positiveelectrode, the initial charge of the negative electrode irreversiblyconsumes lithium so that upon subsequent discharge, the negativeelectrode cannot supply enough lithium to supply the positive electrodewith sufficient lithium to satisfy the full lithium accepting capacityof the positive electrode. This results in a waste of positive electrodecapacity, which correspondingly adds weight that does not contribute tocycling. Also, it has been found that lithium deficiencies can bedisadvantageous for cycling of mixed phase high capacity cathode activematerials as noted in the '703 application cited above. Supplementallithium can be used to compensate for lithium removed from cyclingavailability due to the irreversible capacity loss, as described furtherabove.

If the negative electrode has a comparable or smaller irreversiblecapacity loss relative to the positive electrode irreversible capacityloss, supplemental lithium may not be as desirable to replace lithiumavailable for cycling which has been lost by the irreversible capacityloss of the negative electrode. High capacity silicon based negativeelectrode active materials with an irreversible capacity loss of about7-15%, which is comparable to the high capacity positive electrodematerials, are described in the last example below. Other high capacitysilicon based active materials with relatively low irreversible capacityloss are described in Cui et al., “Carbon-Silicon Core-Shell Nanowiresas High Capacity Electrode for Lithium Ion Batteries,” Nano Letters Vol.9 (9), pp 3370-3374 (2009), incorporated herein by reference.

Whether or not supplemental lithium is included in the battery, theenergy density of the battery can be relatively higher if the cyclingcapacities of the two electrodes at a low rate over the full activationdepth of discharge are balanced with a small to moderate excess ofnegative electrode capacity. In general, an excess of positive electrodecapacity with available cycling lithium may be undesirable since lithiummetal can plate on the negative electrode during charging, and theplated metal can compromise the electrical separation of the electrodesto short circuit the cell. However, it has been discovered that animproved energy density for the battery can be achieved by balancing theelectrodes at a moderate discharge rate over a reduced depth ofdischarge rather than at a low discharge rate can result in a reducedwaste of electrode capacity.

The initial activation cycle and the first few cycles generally areperformed at relatively low rates of charge and discharge, such as C/10or slower. Due to the irreversible changes to the materials during thefirst activation cycle, low rates can reduce further changes to thematerials that may be undesirable. However, for practical applicationssuch as electric vehicle applications, the batteries generally aredischarged during use at moderate rates. A C/3 rate has been selected insome contexts as a moderate rate for testing battery cycling. Thecapacity of the electrodes is rate dependent, and for the high capacitymaterials described herein, the positive electrode active material has acapacity that decreases more at higher rates relative to the decrease incapacity of the negative electrodes at higher rates. Also, to achievedesired long term cycling at an acceptable drop in capacity, batteriesare generally cycled over a reduced depth of discharge. Very long termcycling with the lithium rich positive electrode materials describedherein has been achieved with an appropriately selected voltage window,as described in published U.S. patent application 2012/0056590 toAmiruddin et al., entitled “Very Long Cycling of Lithium Ion Batterieswith Lithium Rich Cathode Materials,” incorporated herein by reference.Thus, it is useful to consider two electrode balances, an initialbalance for the first cycle, and an activated balance at moderate ratesat a reduced depth of discharge.

In particular, the battery can be activated at a low rate of charge anddischarge during the first cycle or first few cycles. Then, theactivated balance of the battery can be considered at a reference rateof C/3, which can be adopted as a standard moderate rate. And forconvenience, the fifth cycle can be selected as a reference cycle inwhich initial changes to the materials have been completed andnegligible cycling fade has taken place for most materials of interest.Capacities of individual electrodes are evaluated with the equivalentelectrode cycled against lithium foil as a suitable reference value asdescribed above. Then, the battery can be balanced to have lithiumplating at low rates during the early cycles, and with no lithiumplating as the battery is cycled at an increased rate and/or over areduced depth of discharge, such as an 80% depth of discharge used as areference. A reduction of the depth of discharge, effectively storessome cyclable lithium on the positive electrode active material duringthe charge of the battery so that this amount of lithium is not platedon the negative electrode during charging. To provide some specificreference values, a voltage window from 4.3V to 1.5V is used as areference for evaluating cycling over a reduced depth of discharge, andresults are presented in the examples for this voltage range. Anincrease of charge and discharge rate similarly result in the effectivestorage of lithium on the positive electrode that is not removed duringdischarge, which the capacity of the negative electrode is changed by asignificantly reduced amount relative to the positive electrode.

The balance can be selected based on the irreversible capacity loss ofthe negative electrode. If the negative electrode has a significantlygreater irreversible capacity loss than the positive electrode, thenegative electrode capacity can generally be balance from about 90% toabout 125% and in further embodiments from about 100% to about 120% ofpositive electrode capacity. Supplemental lithium can be added asdescribed above, although this can result in plating of lithium on thenegative electrode with cycling over the full voltage window of thebattery. If the negative electrode has a similar irreversible capacityloss as the positive electrode active material, the negative electrodecan be balanced from about 75% to about 99.5% and in further embodimentsfrom about 85% to about 98% of the positive electrode irreversiblecapacity loss to achieve a higher energy density, although lithiumplating can take place with cycling over the full voltage window of thebattery. As described in the following, subsequent cycling over areduced voltage window can eliminate lithium plating over the longerterm cycling of the battery. A person of ordinary skill in the art willrecognize that additional ranges of balance within the explicit rangesabove are contemplated and are within the present disclosure.

For other relative values of irreversible capacity loss, appropriatevalues can be extrapolated from these values. For example, duringactivation of the battery in the first charge, the balance can beselected to have plating of lithium metal, that is eliminated duringsubsequent cycling at a greater rate with a reduced depth of discharge,such as a C/3 rate between 4.3V and 1.5V. With respect to the lithiummetal plating regardless of the irreversible capacity loss, the batterycan have a first activation cycle negative electrode charge capacityfrom about 72.5% to about 99.5%, in some embodiments from about 75% toabout 97.5% and in additional embodiments from about 77% to about 95% ata rate of C/20 from the open circuit voltage of the initially assembledbattery to 4.6V relative to the sum of the initial first cycle positiveelectrode charge capacity at a rate of C/20 from the open circuitvoltage to 4.6V plus the oxidative capacity of any supplemental lithium.A person of ordinary skill in the art will recognize that additionalranges of balance within the explicit ranges above are contemplated andare within the present disclosure. Such under-balancing of the negativeelectrode during formation makes more effective use of the batterycomponents during operational cycling over a reduced voltage window sothat a smaller and lighter battery can be used to achieve the sameperformance as a battery with greater negative electrode capacity. Asnoted above, supplemental lithium can be included to provide appropriateamounts of lithium available for cycling.

Battery Performance

Batteries have been formed with high energy formats suitable forcommercial applications, such as electric vehicle applications based onhigh capacity positive electrodes and high capacity negative electrodes.Very good cycling performance has been obtained, especially forembodiments with supplemental lithium. Electrode designs have beendeveloped to take advantage of the high capacity materials, as describedabove.

The lithium ion secondary battery disclosed herein can have a dischargeenergy density of at least about 250 Wh/kg at C/20 when discharged from4.6V to 1.5V. In some embodiment, the battery has a discharge energydensity of at least about 300 Wh/kg, and in other embodiments from about325 Wh/kg to about 430 Wh/kg at a C/20 rate from 4.6V to 1.5V.Similarly, the battery can exhibit a discharge energy density of atleast about 230 Wh/kg, in other embodiments at least about 250 Wh/kg andin further embodiments from about 280 Wh/kg to about 410 Wh/kg at a C/3rate from 4.5V to 1.5V. With respect to battery volume, the lithium ionbatteries can have a volumetric energy density of at least about 600Wh/M (watt hours/liter), in further embodiments from about 650 Wh/l toabout 925 Wh/l and in additional embodiments from about 700 Wh/M toabout 900 Wh/l at a rate of C/20 from 4.6V to 1.5V. Similarly, thebattery can exhibit a volumetric energy density of at least about 450Wh/l, in other embodiments at least about 500 Wh/l and in furtherembodiments from about 600 Wh/l to about 800 Wh/l at a C/3 rate from4.5V to 1.5V. The batteries also exhibit very good cycling performance.In some embodiments, the batteries exhibit a discharge capacity at cycle100 of at least about 90% of the 6th cycle capacity discharged at C/3from 4.5V to 1.5V, in other embodiments at least about 92% and inadditional embodiments at least about 94% at the 100th cycle relative tothe 6th cycle. Also, capacity fade with cycling can be reduced bycycling over a reduced voltage window. Thus, in some embodiments, thebatteries exhibit a discharge capacity at cycle 100 of at least about90% of the 6th cycle capacity discharged at C/3 from 4.35V to 1.5V, inother embodiments at least about 92% and in additional embodiments atleast about 94% at the 100th cycle relative to the 6th cycle. In someembodiments, the battery exhibits a 500th cycle energy density of atleast about 200 Wh/kg, in further embodiments at least about 225 Wh/kgwhen discharged at a rate of C/3 from 4.3V to 1.5V. A person of ordinaryskill in the art will recognize that additional ranges of energydensities within the explicit ranges above are contemplated and arewithin the present disclosure.

EXAMPLES

To test positive electrodes and negative electrodes with differentcompositions, batteries were constructed and tested against lithium foilas the counter electrode. Other batteries were then formed with highcapacity positive electrodes with the high capacity negative electrodesat different excess anode capacity with or without supplemental lithiumto construct coin cell batteries. The general procedure for formation ofthe coin batteries is described in the following discussion.Additionally, the positive electrodes and the negative electrodes atdifferent excess anode capacity with or without supplemental lithiumwere assembled to pouch cell batteries. The batteries were cycled over arelevant voltage range for a commercial battery. The individual examplesbelow describe formulation of the electrodes and the batteries and theperformance results from the batteries. The batteries with silicon basednegative electrode described herein in general were cycled by chargingfrom the open circuit voltage to 4.6V and discharging between 4.6V and1.5V in the first formation cycle and between 4.5V and 1.5V in the cycletesting for batteries with high capacity manganese rich (HCMR™) positivecounter electrode or between 0.005V-1.5V for batteries with lithium foilcounter electrode. The batteries were discharged at a rate of C/10, C/5,and C/3 for the 1st and 2nd cycles, for the 3rd and 4th cycles, and forsubsequent cycles, respectively. All percentages reported in theexamples are weight percents.

Negative electrodes were formed from silicon based active materials,which are described further below. In general, a powder of the siliconbased active material was mixed thoroughly with an electricallyconductive carbon additive, such as a blend of acetylene black (Super P®from Timcal, Ltd., Switzerland) with either graphite or carbonnanotubes, to form a homogeneous powder mixture. Separately, polyimidebinder was mixed with N-methyl-pyrrolidone (“NMP”) (Sigma-Aldrich) andstirred overnight to form a polyimide-NMP solution. The homogenouspowder mixture was then added to the polyimide-NMP solution and mixedfor about 2 hours to form homogeneous slurry. The slurry was appliedonto a copper foil current collector to form a thin, wet film and thelaminated current collector was dried in a vacuum oven to remove NMP andto cure the polymer. The laminated current collector was then pressedbetween rollers of a sheet mill to obtain a desired laminationthickness. The dried laminate contained at least 75 wt % porous siliconbased active material and at least 2 wt % polyimide binder. Theresulting electrodes were assembled with either a lithium foil counterelectrode or with a counter electrode comprising a lithium metal oxide(LMO), such as high capacity manganese rich (HCMR™) lithium metal oxidematerial as synthesized in the '853 application, the '332 application,and the '981 application referenced above.

The examples below in general use HCMR™ positive material approximatelydescribed by the formula xLi₂MnO₃.(1−x)LiNi_(u)Mn_(v)Co_(w)O₂ wherex=0.3 or 0.5. Positive electrodes were formed from the synthesized HCMR™powder by initially mixing it thoroughly with conducting carbon black(Super PT from Timcal, Ltd, Switzerland) and either graphite (KS 6™ fromTimcal, Ltd) or carbon nanotubes to form a homogeneous powder mixture.Separately, Polyvinylidene fluoride PVDF (KF1300™ from Kureha Corp.,Japan) was mixed with N-methyl-pyrrolidone (Sigma-Aldrich) and stirredovernight to form a PVDF-NMP solution. The homogeneous powder mixturewas then added to the PVDF-NMP solution and mixed for about 2 hours toform homogeneous slurry. The slurry was applied onto an aluminum foilcurrent collector to form a thin, wet film and the laminated currentcollector was dried in vacuum oven at 110° C. for about two hours toremove NMP. The laminated current collector was then pressed betweenrollers of a sheet mill to obtain a desired lamination thickness. Thedried positive electrode comprised at least about 75 weight percentactive metal oxide, at least about 1 weight percent graphite, and atleast about 2 weight percent polymer binder. Positive electrodes usingHCMR™ positive electrode active material are generally referred to asHCMR™ electrodes.

For batteries with the lithium foil counter electrodes, the electrodeswere placed inside an argon filled glove box for the fabrication of thecoin cell batteries. Lithium foil (FMC Lithium) having thickness ofroughly 125 micron was used as a negative electrode. A conventionalelectrolyte comprising carbonate solvents, such as ethylene carbonate,diethyl carbonate and/or dimethyl carbonate, was used. A trilayer(polypropylene/polyethylene/polypropylene) micro-porous separator (2320from Celgard, LLC, NC, USA) soaked with electrolyte was placed betweenthe positive electrode and the negative electrode. A few additionaldrops of electrolyte were added between the electrodes. The electrodeswere then sealed inside a 2032 coin cell hardware (Hohsen Corp., Japan)using a crimping process to form a coin cell battery. The resulting coincell batteries were tested with a Maccor cycle tester to obtaincharge-discharge curve and cycling stability over a number of cycles.

For batteries with the HCMR™ counter electrodes, the silicon oxide basedelectrode and the HCMR™ electrode were placed inside an argon filledglove box. An electrolyte was selected to be stable at high voltages,and appropriate electrolytes with halogenated carbonates, e.g.,fluoroethylene carbonate are described in the '367 application. Based onthese electrodes and the high voltage electrolyte, the coin cellbatteries were completed with separator and hardware as described abovefor the batteries with the lithium foil electrode. During the firstcycle, the batteries were charged to 4.6V, and in subsequent cycles, thebatteries were charged to 4.5V.

Some of the batteries fabricated from a silicon based negative electrodeand a HCMR™ positive electrode can further comprise supplementallithium. In particular, a desired amount of SLMP® powder (FMC Corp.,stabilized lithium metal powder) was loaded into a vial and the vial wasthen capped with a mesh comprising nylon or stainless steel with a meshsize between about 40 μm to about 80 μm. SLMP® (FMC corp.) was thendeposited by shaking and/or tapping the loaded vial over a formedsilicon based negative electrode. The coated silicon based negativeelectrode was then compressed to ensure mechanical stability.

Batteries fabricated from a silicon based negative electrode and a HCMR™positive electrode can be balanced to have excess negative electrodematerial. The balancing was based on the ratio of the first cyclelithium insertion capacity of the silicon based negative electrode tothe total available lithium in the battery which is the sum of theoxidation capacity of the supplemental lithium and the theoreticalcapacity of the HCMR™ positive electrode. In particular, for a givensilicon based active composition, the insertion and extractioncapacities of the silicon based composition can be evaluated in abattery setting. For example, a battery that has a positive electrodecomprising the silicon based active material with a counter lithium foilnegative electrode can be constructed. The insertion and extractioncapacities of the silicon based composition in the electrode equals tothe first cycle battery capacity measured when lithium isintercalated/alloyed to the porous silicon based electrode to 5 mV andde-intercalated/de-alloyed to 1.5V at a rate of C/20. Specific values ofthe excess negative electrode balance are provided in the specificexamples below. For batteries containing supplemental lithium, theamount of supplemental lithium was selected to approximately compensatefor the irreversible capacity loss of the negative electrode.

Example 1 Construction and Performance Evaluation of High CapacityNegative Electrodes

To test the impact of different relative amounts of anode composition,binder and conducting additives on the cycling performance of anelectrode, electrodes 1-4 with different composition as outlined inTable 1 below were constructed, using a procedure outlined above. Thenegative electrode active material used is a SiO—Si—C composite, such asdescribed in the '708 application referenced above. The polymeric binderused was a polyimide from a commercial supplier as described above. Theelectrically conductive material for these batteries was carbonnanotubes, which were obtained from a commercial supplier. The amount ofSiO—Si—C composite in electrodes 1 to 4 is varied in the range of 80% to90%.

TABLE 1 Electrode % Active Material % Carbon nanotubes 1 85 a 2 80 a 380 >a  4 90 0

The electrodes were cycled against a lithium foil counter electrode over40 cycles at a rate of C/20 for 1st cycle, C/10 for 2nd cycle, C/5 for3rd cycle, and C/3 for subsequent cycles, and the discharge capacity ofthe electrodes versus cycle number is plotted in FIG. 3. As shown inFIG. 3, electrode 1 with 85% SiO—Si—C composite gave the best cyclingperformance and higher capacity compared to electrodes with othercompositions. Electrode 4 with 90% SiO—Si—C composite and 10% binder andno conductive additive did not show good cycling performance and fadedrapidly.

To test the effect of density on the silicon-based electrodeperformance, electrodes 5-7 with active material densities of 0.9 g/mL,1 g/mL, and 1.2 g/mL respectively were constructed using the electrodeformulation of electrode 1 above. The electrodes were cycled against alithium foil counter electrode over 40 cycles at a rate of C/10 1stcycle, C/5 2nd cycle, and C/3 subsequent cycles and the dischargecapacity of the electrodes versus cycle number is plotted in FIG. 4. Asshown in FIG. 4, electrode 5 with the lowest density of 0.9 g/mL showedthe best cycling performance compared to the other two electrodes.

Detailed information with regard to the compositions and formation ofsilicon based anode materials are disclosed in the '096 application, the'294 application, and the '708 application referenced above. To comparethe electrode performance of different silicon based negative electrodeactive materials, electrodes 8-10 made with porous silicon basedmaterial, SiO—Si—C composite, and SiO—C composite respectively wereconstructed and tested. Electrode 8 comprised porous silicon basedmaterial, Super-P as conductive additive, and binder. Electrode 9comprised SiO—Si—C composite anode material in an electrode formulationcorresponding to electrode 1 above. Electrode 10 comprised SiO-Ccomposite anode material with Super-P as conductive additive, andbinder. Electrodes 8-10 had an electrode density from 0.5 g/mL to 1.2g/mL and a loading level of 2.0 mg/cm² to 4.5 mg/cm².

The electrodes were cycled against a lithium foil counter electrode over40 cycles and the capacity of the electrodes versus cycle number isplotted in FIG. 5. The batteries were cycled at a rate of C/20 for thefirst cycle, at C/10 for the second cycle, at C/5 for the third and theforth cycles, and at C/3 for the remaining cycles. As shown in FIG. 5,electrode 8 made with porous silicon based material showed the highestcapacity and the best capacity retention of all three electrodes.Electrode 9 made with SiO—Si—C composite showed stable cycling life andgood capacity retention when the rate is changed from C/20 to C/3.

Example 2 Construction and Performance Evaluation of High CapacityPositive Electrodes

Positive electrodes that have high capacity, high electrodeconductivity, high electrode loading balanced with high electrodedensity have been constructed and tested for cycling performance againsta lithium foil counter electrode. The effects of carbon nanotubes as anelectrically conductive component were also tested. The lithium metaloxide used for the positive electrode can be approximately representedby the formula Li₂MnO₃.(1−x)LiNi_(u)Mn_(v)Co_(w)O₂. A first compositionhad x=0.5 and a second composition had x=0.3. The compositions had ametal halide coating. A discussion of the synthesis and testing of arange of cathode active materials with similar stoichiometries with orwithout additional oxide or halide coatings can be found in publishedU.S. patent application 20111/0052981A to Lopez et al., entitled“Layer-Layer Lithium Rich Complex Metal Oxides With High SpecificCapacity And Excellent Cycling,” incorporated herein by reference.

To test the effect of different conductive additive on the positiveelectrode performance, electrodes 11 and 12 with an active materialloading level of about 22 mg/cm² were constructed. Electrode 11 usedSuper-P and KS-6 as conductive additive while electrode 12 used Super-Pand carbon nanotubes. Both electrodes had approximately equivalentformulations with >90% positive electrode active material, <5% PVDFbinder and <5% total conductive additives. The electrodes were cycledagainst a lithium foil counter electrode from 2V to 4.6V over 20 cyclesat a rate of C/20 for 1st cycle, C/10 for 2nd and 3rd cycles, C/5 for4th and 5th cycles, and C/3 for subsequent cycles, and the capacity ofthe electrodes versus cycle number is plotted in FIG. 6. As shown inFIG. 6, electrode 12 with the Super-P and carbon nanotubes showed thebetter cycling performance compared to the electrode 11 with KS-6graphite in place of carbon nanotubes.

To test the effect of different electrode loading levels on cyclingperformance, electrodes 13-15 with a loading level of 13 mg/cm², 18mg/cm², and 26 mg/cm² were constructed. All the electrodes werecalendared to an approximately equivalent active material electrodedensity of <3 g/mL and had approximately equivalent electrodeformulations with >90% positive electrode active material, <5% totalconductive additives (carbon nanotube and Super-P), and <5% binder. Theelectrodes were cycled against a lithium foil counter electrode over 40cycles at a rate of C/10, C/5, and C/3 for the 1^(st), 2^(nd) and 3rd,and for subsequent cycles, respectively and the capacity of theelectrodes versus cycle number is plotted in FIG. 7. As shown in FIG. 7,electrodes 13 and 14 with loading levels 13 mg/cm² and 18 mg/cm²respectively cycled well while electrode 15 with loading level 26 mg/cm²faded and failed after 25 cycles.

To test the balance of electrode density with electrode loading level,electrode 16 with a loading level of 26 mg/cm² and an active materialdensity of about 2.4 g/mL was constructed. The electrode had >90%positive electrode active material, <5% total conductive additives(carbon nanotube and Super-P), and <5% binder. The electrode was cycledagainst a lithium foil counter electrode over 20 cycles at a rate ofC/20 for the 1st cycle, C/10 for the 2nd cycle, C/5 for the 3rd cycle,and C/3 for subsequent cycles, and the charge capacity and dischargecapacity of the electrode versus cycle number is plotted in FIG. 8. Asshown in FIG. 8, electrode 16 has good cycling performance out to 50cycles even with a high loading level of 26 mg/cm² when the density wasreduced to 2.4 g/mL, which corresponds to a thicker electrode.

Example 3 Balance of Positive Electrode and Negative ElectrodeCapacities with or without Supplemental Lithium

Batteries 1-6 outlined in Table 2 below were constructed with differentcapacity balances of HCMR™ positive electrode 12 of example 2 andSiO—Si—C composite negative electrode 1 of example 1 with or withoutsupplemental lithium to test for cycling performance. Batteries 1-4 wereconstructed with excess negative electrode capacity 10%, 20% a, 30% and40% over the positive electrode capacity, respectively. Supplementallithium is added to batteries 1-4 with a capacity equivalent to thedifference between the capacities of the anode and the cathode. Thus,battery 1 has the least amount of supplemental lithium, and battery 4has the greatest amount of supplemental lithium. Batteries 5 and 6 wereconstructed with balances of 5% and 30% excess negative electrodecapacity relative to the positive electrode capacity respectivelywithout supplemental lithium. The amount of supplemental lithium addedinto batteries 1-4 is estimated to compensate for the excess anodecapacity of the negative electrode. For example battery 1 with 10% anodeexcess has supplemental lithium in an amount with an oxidation capacitythat is the difference between the anode and cathode capacities, whichis about 10% excess over the cathode capacity. While battery 4 with 40%excess anode has supplemental lithium in an amount with an oxidationcapacity equivalent to the difference between the anode and cathodecapacities which is about 40% excess over the cathode capacity.

TABLE 2 % excess negative Supplemental IRCL in the first Batteryelectrode capacity lithium cycle % 1 10 Yes 14.0 2 20 Yes 13.1 3 30 Yes12.3 4 40 Yes 12 5 5 No 26.6 6 30 No 29.1

The batteries were cycled at a rate of C/20 for 1st cycle, C/10 for 2ndand 3rd cycles, C/S for 4th and 5th cycles, and C/3 for subsequentcycles, and the results are shown in FIG. 9. As shown in FIG. 9, forbatteries 1-4 with supplemental lithium, batteries with higher anodeexcess have better cycling performance. Battery 4 with 40% excess anodefor example has a capacity fade of <1% during 90 charge/discharge cyclescompared to the first C/3 cycle capacity. In comparison, batteries 5 and6 without any supplemental lithium showed rapid fading in capacity,which may be attributable to a significant capacity loss from thecathode into the anode in the first cycle that is evident from the firstcycle IRCL in the batteries 5 and 6 shown in table 2 above.

Example 4 Construction and Cycling Performance Evaluation of Pouch CellBatteries

Batteries with compositions of battery 4 of example 3 above wereconstructed into pouch cell format. These pouch cell batteries wereconstructed to have a variety of overall capacities and were then testedfor cycling performance. Pouch cell batteries 7 and 8 with a designcapacity of roughly 10 Ah were cycled at C/10 for the first cycle, atC/5 for the next three cycles, and at C/3 for the remaining cycles, at avoltage range of 1.5V to 4.6V for the first cycle followed by a voltagerange of 1.5V to 4.5V for the subsequent cycles. The cathode electrodeused has a loading level of >16 mg/cm² and the anode used has a loadinglevel of >3.5 mg/cm². Battery 7 has 38% excess anode and supplementallithium. Battery 8 has 10% excess anode with no supplemental lithium.Battery 7 with supplemental lithium showed excellent cycling performancewith an energy density of about 270 Wh/Kg at C/10 and 246 Wh/Kg at thefirst C/3 rate and has a volume energy density of 400 Wh/L. As shown inFIG. 10, battery 7 finished 140 cycles with 90% capacity remaining after140 cycles while battery 8 without supplemental lithium has a rapidcapacity fade and the capacity fell to less than 50% after 140 cycles.

Pouch cell battery 9 with a design capacity of roughly 20 Ah was cycledat C/20 for the first cycle, at C/10 for the next two cycles, at C/S forthe next two cycles, and at C/3 for the remaining cycles at a voltagerange of 1.5V to 4.6V for the first cycle followed by a voltage range of1.5V to 4.5V for subsequent cycles. The cathode had a loading levelof >20 mg/cm², and the anode had a loading level of >4.5 mg/cm². Battery9 had 20% excess anode and supplemental lithium to compensate for theIRCL of the battery. As shown in FIG. 11( b) battery 9 gave an energydensity of 330 Wh/Kg at C/20, 296 Wh/Kg at the first C/3 cycle, andabout 65% efficiency at C/3 after 200 cycles. As shown in FIG. 11( a),the capacity of battery 9 maintained above 14000 mAh after 200charge/discharge cycles.

Pouch cell battery 10 with a design capacity of roughly 48 Ah was cycledat C/20 for the first cycle, at C/10 for the next cycle, C/3 for thenext two cycles with the first four cycles from 4.6V to 1.5V, and at C/3from 4.3V to 1.5V for the remaining cycles. The cathode had a loadinglevel of >25 mg/cm², and the anode had a loading level of >4.5 mg/cm².Battery 10 has no excess anode balance and the supplemental lithium isloaded to compensate for about 60% of anode irreversible capacity loss.As shown in FIG. 12( b) battery 10 gave an energy density of 430 Wh/Kgat C/20, 410 Wh/Kg at C/10, 392 Wh/Kg at the first C/3 cycle, 310 Wh/Kgat the first C/3 from 4.3V to 1.5V, and about 68% efficiency at C/3 from4.3V to 1.5V after 500 cycles. As shown in FIG. 12( c) battery 10 gavean energy density of about 850 Wh/L at C/20, about 805 Wh/L at C/10,about 760 Wh/L at the first C/3 cycle, about 605 Wh/L at first C/3 from4.3V to 1.5V, and about 400 Wh/L at C/3 from 4.3V to 1.5V after 500cycles. As shown in FIG. 12( a), the capacity of battery 10 maintainedabove 2400 mAh after 500 cycles at C/3 from 4.3V to 1.5V.

The embodiments above are intended to be illustrative and not limiting.Additional embodiments are within the claims. In addition, although thepresent invention has been described with reference to particularembodiments, those skilled in the art will recognize that changes can bemade in form and detail without departing from the spirit and scope ofthe invention. Any incorporation by reference of documents above islimited such that no subject matter is incorporated that is contrary tothe explicit disclosure herein.

What is claimed is:
 1. A lithium ion secondary battery comprising apositive electrode, a negative electrode, and a separator between thepositive electrode and the negative electrode, wherein the negativeelectrode comprises a high capacity negative electrode active materialwith a specific capacity of at least 700 mAh/g at a discharge rate ofC/3, has a density in the range of about 0.4 g/mL to about 1.3 g/mL, andhas a loading level of negative electrode active material that is atleast 1.5 mg/cm², and wherein the battery has a discharge energy densityat the 50th charge-discharge cycle of at least about 250 Wh/kg at C/3when discharged from 4.5V to 1.5V.
 2. The battery of claim 1 wherein thepositive electrode comprises about 90 wt % to about 96 wt % positiveelectrode active material, about 2 wt % to about 6 wt % polymericbinder, and about 0.5 wt % to 8 wt % conductive additive.
 3. The batteryof claim 2 wherein the conductive additive comprises carbon fibers,carbon nanotubes, graphene, graphite, carbon black, or a combinationthereof.
 4. The battery of claim 1 wherein the positive electrodecomprises a positive electrode active material that is approximatelyrepresented by the formula Li_(1+b)Ni_(α)Mn_(β)Co_(γ)A_(δ)O_(2−z)F_(z),where b ranges from about 0.01 to about 0.3, α ranges from about 0 toabout 0.4, β range from about 0.2 to about 0.65, γ ranges from 0 toabout 0.46, δ ranges from 0 to about 0.15 and z ranges from 0 to about0.2 with the proviso that both α and γ are not zero, and where A is Mg,Sr, Ba, Cd, Zn, Al, Ga, B, Zr, Ti, Ca, Ce, Y, Nb, Cr, Fe, V, Li orcombinations thereof.
 5. The battery of claim 1 wherein the positiveelectrode has a density in the range of about 2.2 g/mL to about 3.3 g/mLand a loading level of positive electrode active material on a currentcollector that is from about 10 mg/cm² to about 30 mg/cm².
 6. Thebattery of claim 1 wherein the negative electrode comprises about 60 wt% to 90 wt % the silicon based negative electrode active material, about8 wt % to 30 wt % a polymeric binder, and about 1 wt % to 15 wt %conductive additive.
 7. The battery of claim 6 wherein the conductiveadditive comprises carbon fibers, carbon nanotubes, graphene, graphite,carbon black, or a combination thereof.
 8. The battery of claim 1wherein the negative electrode comprises a silicon based material whenmeasured against a lithium metal counter electrode having a first cycleC/10 intercalation/alloying capacity from 1.5V to 5 mV in the range ofabout 2000 mAh/g to about 3900 mAh/g and first cycle C/10deintercalation/dealloying capacity from 5 mV to 1.5V in the range ofabout 1300 mAh/g to about 2500 mAh/g, a C/3 deintercalation/dealloyingcapacity from 5 mV to 1.5V in the range of about 1000-2400 mAh/g, and anirreversible capacity loss of less than about 35%.
 9. The battery ofclaim 1 further comprising supplemental lithium in an amount with anoxidation capacity corresponding to 5% to 150% of the irreversiblecapacity loss of the negative electrode and wherein the total availablelithium in the battery is the sum of the oxidation capacity of thesupplemental lithium and the positive electrode theoretical capacity.10. The battery of claim 1 wherein the positive electrode has a densityin the range of about 2.2 g/mL to about 2.8 g/mL and a loading level inthe range of about 17 mg/cm² to about 27 mg/cm², wherein the positiveelectrode and the negative electrode each comprise carbon nanotubes, andwherein the battery has a discharge energy density at the 75thcharge-discharge cycle of at least about 250 Wh/kg at C/3 whendischarged from 4.5V to 1.5V.
 11. The battery of claim 1 wherein thebattery has a discharge energy density at the 50th charge-dischargecycle of at least about 250 Wh/kg at C/3 when discharged from 4.5V to1.5V.
 12. The battery of claim 1 wherein after an initial activationcharge the battery has a negative electrode capacity of about 75% toabout 99.5% at a rate of C/20 from the open current voltage to 4.6Vrelative to the sum of the positive electrode capacity at a rate of C/20from the open current voltage to 4.6V plus the oxidation capacity of anysupplemental lithium.
 13. The battery of claim 1 wherein the battery hasa volumetric energy density of at least about 600 Wh/l at a rate of C/20from 4.6V to 1.5V.
 14. A positive electrode for a lithium ion secondarybattery comprising: from about 90 wt % to about 96 wt % positiveelectrode active material, from about 2 wt % to about 6 wt % polymericbinder, and from about 0.5 wt % to about 8 wt % conductive additivecomprising carbon nanotubes, carbon nanofibers, graphene or combinationsthereof, wherein the positive electrode has a specific dischargecapacity of at least 180 mAh/g at C/3 from 4.6V to 2V against lithium,wherein the positive electrode active material is loaded on a currentcollector and the loading level of positive electrode active material onthe current collector is from about 10 mg/cm² to about 30 mg/cm² andwherein the electrode has a density in the range of about 2.2 g/mL toabout 3.3 g/mL.
 15. The positive electrode of claim 14 when measuredagainst a lithium metal counter electrode having a first cycle chargecapacity to 4.6V in the range of about 250 mAh/g to about 320 mAh/g anddischarge capacity from 4.6V to 2V in the range of about 230 mAh/g toabout 290 mAh/g at C/10 and a C/3 discharge capacity from 4.6V to 2V inthe range of about 180 mAh/g to about 270 mAh/g.
 16. The positiveelectrode of claim 14 further comprising about 1 wt % to about 5 wt % ofan additional conductive additive that comprises carbon nanostructuredcarbon, powdered graphite, carbon black, or a combination thereof. 17.The positive electrode of claim 14 wherein the positive electrode activematerial approximately represented by the formulaLi_(1+b)Ni_(α)Mn_(β)Co_(γ)A_(δ)O_(2−z)F_(z), where b ranges from about0.01 to about 0.3, α ranges from about 0 to about 0.4, β range fromabout 0.2 to about 0.65, γ ranges from 0 to about 0.46, δ ranges from 0to about 0.15 and z ranges from 0 to about 0.2 with the proviso thatboth a and y are not zero, and where A is Mg, Sr, Ba, Cd, Zn, Al, Ga, B,Zr, Ti, Ca, Ce, Y, Nb, Cr, Fe, V, Li or combinations thereof.
 18. Anegative electrode for a lithium ion secondary battery comprising: fromabout 60 wt % to about 90 wt % of a high capacity negative electrodeactive material, from about 8 wt % to 30 wt % of a polymeric binder, andfrom about 1 wt % to 15 wt % conductive additive comprising carbonnanotubes, carbon fibers, graphene or combinations thereof, wherein theelectrode has a specific deintercalation/dealloying capacity from about5 mV to 1.5V against lithium of at least 700 mAh/g at C/3, wherein theloading level of negative electrode active material is at least 1.5mg/cm², and wherein the electrode has a density in the range of about0.4 g/mL to about 1.3 g/mL.
 19. The negative electrode of claim 18wherein the silicon based negative electrode active material is a poroussilicon based material having a first cycle C/10 Liintercalation/alloying capacity to 5 mV in the range of about 2600 mAh/gto about 3900 mAh/g and a Li deintercalation/dealloying capacity in therange of about 2200 mAh/g to about 3300 mAh/g from 5 mV to 1.5V, a C/3Li deintercalation/dealloying capacity in the range of about 1800 mAh/gto about 2800 mAh/g from 5 mV to 1.5V, and an irreversible capacity lossof less than about 35%.
 20. The negative electrode of claim 18 whereinthe silicon based negative electrode active material is a SiO-carboncomposite having a first cycle C/10 Li intercalation/alloying capacityto 5 mV in the range of about 1800 mAh/g to about 2600 mAh/g and a Lideintercalation/dealloying capacity in the range of about 1400 mAh/g toabout 2000 mAh/g from 5 mV to 1.5V, a C/3 Li deintercalation/dealloyingcapacity in the range of about 1000 mAh/g to about 1900 mAh/g from 5 mVto 1.5V, and an irreversible capacity loss of less than about 35%. 21.The negative electrode of claim 18 wherein the silicon based negativeelectrode active material is a SiO—Si-carbon composite having a firstcycle C/10 Li intercalation/alloying capacity to 5 mV in the range ofabout 1800 mAh/g to about 3000 mAh/g and a Li deintercalation/dealloyingcapacity in the range of about 1500 mAh/g to about 2500 mAh/g from 5 mVto 1.5V, a C/3 Li deintercalation/dealloying capacity in the range ofabout 1300 mAh/g to about 2200 mAh/g from 5 mV to 1.5V, and anirreversible capacity loss of less than about 35%.
 22. The negativeelectrode of claim 18 further comprising from about 1 wt % to about 15wt % of an additional electrically conductive additive comprisingpowdered graphite, nanostructured carbon, carbon black or a combinationthereof.
 23. The negative electrode of claim 18 further comprisingsupplemental lithium in an amount with an oxidation capacitycorresponding to from about 5% to about 120% of the irreversiblecapacity loss of the negative electrode.